So, most all of you have probably seen the new Sisters of Battle codex from White Dwarf by now. If you haven't... well, it's not hard to find if you care to look. And, while it's undeniably worse in many respects than the old WH book, pining for the old isn't going to get us anywhere; my Tyranids would like 114pt Carnifexes back, but that ain't happening, so best to make do with what we have now. In that respect, there are useful things in the new book, though it's doubtful they'll be able to live up to the old one's level of utility. However, it's worth taking a look at what we can do.
First of all, Faith is super-different, which I'm sure everyone knows by now. The long and short of it is that the bigger the game goes, the less useful Faith ends up being overall, since you have a static amount of it to distribute amongst your units. However, it's also a renewable resource, so no longer is there an impetus to hem and haw over whether to spend it. By my interpretation of the rule, there is nothing stopping you from attempting a particular Act of Faith several times if you fail the first one- indeed, even if you succeed the first one, though the benefits are (mostly) non-cumulative. However, doubtless GW will FAQ this away, so I wouldn't count on it.
(The reason I make this interpretation is that it is clearly possible to make more than one Act of Faith roll for a single unit- this is implied in the fact that Independent Characters, who become part of a unit, can make Act of Faith rolls of their own. Since it never specifies, unlike IG Orders, that you must resolve all of one unit's Faith and then move on to the next, you would appear to be able to choose a unit more than once to make a Faith roll. This being the case, nothing prevents you from choosing that unit again if they fail the first time, until you run out of Faith at least.)
They also get an army-wide 6++ save. This is... pretty worthless, for the most part, but there are a select few units it benefits, which we'll talk about in their respective entries. However, for the most part cover saves and 3+ armor mean that you will very rarely get to roll it, and when you do it will almost always let you down, and when it doesn't it will rarely make a difference anyways. If you're getting Power Fisted to death by some Marines, staving off one wound is not going to turn things from a loss to a win.
Now, let's take a look at the girls.
HQ
Saint Celestine
GW, like the often do, made a little boo-boo with Essy Cee; she's listed as having the Independent Character rule in her monster manual entry, but her army listing does not have it. I will be assuming here that she is not, in fact, an IC; if she is, it ups her value a pretty significant chunk. Anyways, the Big Lady here is quite a beast in close combat, coming with ridiculous WS and BS skills (though she can't use the latter), 2+/4++, a 4+ poisoned power weapon, and a jump pack, along with Fearless and grenades. She's also packing I7 and A5, pretty beefy numbers. Her sword can shoot a Heavy Flamer, but that's only meh. Her big deal is coming back to life every turn on a 4+, which will prove incredibly annoying for your opponent, as there's no way to stop it. On the downside, she's T3 and W3, so expect to see her get drowned in attacks reasonably often or just bite it to failing a save against a Monstrous Creature, Relic Blade, or Power Fist; despite that, she is something that most units don't really want to tangle with and you don't really have to worry about losing her, so she can charge in and hold up scary/shooty units at every possible opportunity. With a very reasonable price tag, she is well worth considering- however, since Jacobus (below) is a must-take, you'll be looking at spending well over 200pts on HQs, which is probably something you can't afford in smaller games.
Canoness
Two single 'n's; remember that. A Cannoness is a female artillery weapon; a Canoness leads a religious order. She has generic HQ stats for her "race," but her Act of Faith is pretty good. Unfortunately +1I just doesn't bring Sisters to the point where they're actually good in a fight, nor does Preferred Enemy, so she isn't a strong candidate on that front. She can get a Combi-weapon, Inferno Pistol, Power Sword, or Chainfist and is Stubborn, but at the end of the day she just doesn't bring a whole lot to the table that you want. Confessors are better melee-buffing HQs and Battle Conclaves are likely to be more useful than Command Squads. She's probably going to get left at home a lot now that she can't get a Jump Pack or 2++, and it's as simple as that.
Sororitas Command Squad
Oh my, how original, Mr. Cruddance. A 115pt five-strong squad that comes with FNP and can take lots of special weapons. To be fair, this is sort of a general thing for Imperials now, so no surprise, but there are a couple catches. One of your dudes has a Laud Hailer, meaning when you spend a Faith within 12" you have a 1/6 chance of getting it back. Second is that you get heavy weapons available to you, which Marines do not. Third, your Act of Faith makes you Relentless (and Move Through Cover, but...); this makes those heavy weapons worth considering. However, since you have to take a Canoness to unlock a squad of them, you're probably not going to end up using them a lot.
(As an aside, Heavy Flamers cost 20pts across the board in this book. It's fucking ridiculous, because they just aren't that good. IG pay similar prices, except on their tanks, where they magically are free. Cruddance, what the hell is wrong with your brain? You also seemed to think Pyrovores and Thorax Swarms were worth a billion points, so it's possible he lives in a world where S5 templates cause instant death or something.)
Arch-Confessor Kyrinov
Nice and cheap, just like Jacobus, and hands out some pretty worthwhile bonuses to the army. 6" Fearless bubble helps with lack of ATSKNF, and he counts as a Loud Hailer (meh) and Simulacra Imperialis (much better, since they're so pricey otherwise.) Also, he's a normal Priest and thus gives rerolls on the charge and has a power weapon that knocks people down to I1, so pairing him up with an assault unit is a pretty decent idea. Comparing him to a normal Confessor... you pay for a power weapon and get all the above, so if you're looking at an HQ beyond Jacobus, this guy and Celestine are basically it.
Uriah Jacobus, Protector of the Faith
*sigh* Well, he gives you a reroll on Faith each turn, so he's required. Aside from that he's also very nice because he gives FNP, +1A, and rerolls on the charge to everyone he's with, so you can't feel too sad about his inclusion. Also he has a big, dumb shotgun or something. You'll probably get sick of seeing this guy's name in army lists, but that's how it is.
Ecclesiarch Confessor
Like the above two named characters, but only marginally cheaper and with very little reason to take one. They, uh, can get an Eviscerator, I guess.
Battle Conclave
Like GK Henchmen, but way more limited. 3-10 models, three choices, all of them melee. Death Cult are still fantastic, all the more so because your HQs are good at enhancing them. Crusaders are good, but you probably won't need many per squad. Arco-Flagellants are pretty meh. Note that none of them have grenades and you can't get any assault transports, so it can be tricky to use them sometimes.
Elites
Ecclesiarchy Priests
Budget versions of the Confessor. Doesn't use a FoC slot, but gives rerolls and can take the same options. Might be useful to hand out bonuses and get the +1 on Acts of Faith for having a character around, but that's about it.
Celestian Squad
Oooh, WS4 and A2, how fancy! But only two special weapons and cost as much as a Grey Hunter, so you're not exactly getting a fantastic deal. +1S and Fearless is cute, But even if you attach a Canoness AND get off both Acts of Faith off AND get the charge, you are merely on par with GH/ASM/etc in terms of fighting. So don't friggin' bother.
Repentia Squad
Jumped about a million notches up, so that's something. A2 with a Chainfist and an act of Faith that lets them get their swing in even when they die means that they will murder most things when they attack; being one of the few units that uses their 6++ (since they have no other armor) and natural FNP makes them able to survive sorta okayish in cases where their Faith doesn't come through. Fleet and Rage make them able to get places, although sometimes a bit awkward to control. The Mistress is pretty blech, but she will at least wound on 4s against most things with a Power Weapon. (Remember you use the majority Ld of the unit just as you would Toughness, not the highest, since it is not a check.) Lacking a transport option of their own, they'll usually have to steal one from someone- Retributors are going to be a favorite here.
Troops
Battle Sister Squad
Guess what, assholes, you lost your only other option and these girls didn't really get any better! Min size ten means they're clumsy to move around and can't have a character for Faith, two special (or one heavy one special) regardless of size makes foot squads utterly worthless (not that they wouldn't be anyways), and their Act of Faith is one of the worst in the book; it can be a shitty version of ATSKNF (you can still get Swept off the field, you can't move the turn you regroup) or can reroll 1s to hit in shooting or melee. Other than that... yeah, nothing. You'll take two squads because you have to and hate yourself for it. Oh, they carry Boltgun + BP now and have grenades, but so the fuck what? It's not like you were in a hurry to charge anyone anyways.
Dedicated Transports
Rhino
It's useful now. Strictly better than the usual Marine ones, since it has a 6++ for when you're not getting cover, but otherwise it's the same metal box everyone gets. This is probably going to be the ride that everyone takes for every squad, since foot SoB just aren't viable.
Immolator
Holy christ, Cruddance, you really went out of your way again this time to take the only good thing in the last book and ruin it, didn't you? The Carnifex is looking less like an accident now. :\ So yeah, it's expensive, it can't move 12" and fire, it doesn't have a fire point, and its upgrade guns are either mediocre (MM) or bad (HB). The only time you'll be considering taking these is with Dominions.
Fast Attack
Seraphim
These managed to stay good. You have HnR (although it's unreliable with I3, but that was true before, too) and can shoot both guns, making you a pretty speedy harassment unit. They can reroll failed Faith tests and their 6++ save, making it slightly less worthless. Their Act of Faith lets them reroll failed wounds, which is pretty good as things go and makes their special pistols extra handy. Oh, right, they can take pairs of Inferno or Flamer pistols, although for some reason the Veteran Sister isn't allowed to take two guns. Huh. Anyways, doing so is exactly as pricey as you'd think it was, since you can use both, so I would be careful about overinvesting in them. You aren't Blood Angels, so don't try and Deep Strike them and shoot, otherwise you're going to end up with a lot of Mishaps.
Dominions
Hey, at least there's one good thing in the codex, you know? At 13pts/body with Scout and double the normal number of special guns, they are sexy as hell. Since their Act of Faith twin-links things, you can probably get away with just running with five of them to gun things down and they'll be pretty reliable about it. As noted above, they are the only unit in the codex that should be considering an Immolator, since they can Scout it forward and possibly do some damage with a Multimelta. I would be inclined to keep them cheap, however.
Heavy Support
Retributors
The poor (wo)man's Long Fangs. Costing the same as basic Sisters, they also get up to four heavy weapons and their Faith gives them Rending, which makes them able to threaten virtually all targets. With the basic squad coming in at 85pts with 4x Heavy Bolter, this is going to be a solid option for most armies. Because they can buy a transport but have no reason to want one, they make an excellent pairing with Repentia; their sisters drive forward and threaten "hard" targets and MEQs while the Retribs sit in the backfield, hosing down weaker models and suppressing transports. You will, in most cases I think, take equal numbers of both of these two squads.
Exorcists
Gained a 6++. Ayup. Still random, still S8 AP1, so will ruin the day of many enemy tanks and MCs. Many people see these as a 3x inclusion like Psyflemen, but given the existence of Retributors I'm more inclined to think they'll be a 1x or 2x at most.
Penitent Engines
Random attacks, Rage, Open-Topped, AV11. That's a pretty unfortunate combination. Yes, you can take them in squads (which isn't completely awful) and they come with twin Heavy Flamers and can really put out some hurt in close combat, but they probably just aren't worth it, since the rest of the army can't effectively support them.
So What's It All Mean?
Looking at our slots, we are pretty locked into choices. HQ is Jacobus plus possibly something else, along with the attendant bodyguards. EL is Repentia (if anything.) TR is obviously some Sisters. FA is either Seraphim for fast-moving harassment or Dominions for fast-moving shooting threats. HS is either Exorcists or Retributors for shooting support. This leaves us with only two real army builds.
Option #1Depending on points, you fit in 2x or 3x of each of the above and call it a day; the list doesn't scale terribly well, since by 1750 you have all your HS, EL, FA, and HQ slots filled, but you are fielding a bunch of squads of diffuse Melta along with some ranged anti-infantry (or tank) support and some major melee threats from the DCA and Repentia, who specialize against different types of targets. It's very aggressive, moving everything forward first (or pre-first) turn and just hoping to blaze the enemy out before they can take real advantage of weak toughness, etc. Faith is prioritized for the Retributors early on and Repentia when they need it, possibly occasionally going to Dominions when a target needs to be taken down.
Jacobus + DCA in Rhino
Repentia, stealing Rhinos from Retributors
Battle Sisters with Melta/Multimelta in Rhinos
Dominions with twin Melta in Rhinos
Retributors donating their Rhinos to above
Option #2Here you play a little more fancy, trying to shield your Seraphim and Celestine early and then use them as disruption in the mid/late game; Meltabunkers and Exorcists try to keep the enemy busy long enough for the Flying Nun to get stuck in and start ruining things. I think this strategy is weaker than the above, but it's also less risky and scales upwards better, since buying additional Seraphim and eventually Celestians is an option. It's even flexible enough with Faith that you might get crazy and drop Jacobus or something, but that's probably not a good idea.
Jacobus with DCA in Rhino
St Celestine
some Celestians with Melta in Rhinos to fill points
Sisters with MM/Melta, probably slightly more than the above list uses
Seraphim with Inferno Pistols
possibly one Dominions squad
Exorcists
possibly one Retributor squad
The new Sisters of Battle book is... ugh, I really don't like it. There's seriously very little you can do with it, my above lists aside; it has absolutely zero depth and does almost nothing better than the Marines books. Your only hope is to try and take advantage of the relative cheapness of many of your squads (100-120pts) to spam out some kind of MSU strategy with a bunch of Melta and other random threats. But guess what, kiddies, that doesn't work so hot for Chaos Space Marines, and they get very similar things for similar prices (160pt troops, forward Melta squads, expensive fire support from the backfield that dies to a few good hits, etc.)
The book isn't absolute trash; there are a few worthwhile things, and you can even feel good about some of the changes that were made, but while the old book was narrow and relied on abusing a small number of things you still had going for you, the new book is the same, except with your strengths toned down. Especially if you play games over 1750, Sisters are really going to struggle until they get a real codex.
