You have no idea how good it feels now that my favorite army, which I started playing around 2002, is no longer called "Witch Hunters." With the upcoming release of the White Dwarf Sisters of Battle codex, the Adepta Sororitas takes its rightful place in the army's titular role.
At this point in time, the Bestiary of our codex is set to be released next week, though some have seen a leaked copy of the list. We know a lot about the units and their special rules, but we know nothing about their points costs, or their squad options, or what all of their wargear does.
I will get us started by analyzing what we know--not every detail, just a quick rundown of how I think the units will work.
Canoness: Not much on her own, but her Act of Faith, giving +1 Initiative and Preferred Enemy could be very useful in assault leading either a command squad or a unit of Celestians.
Sororitas Command Squad: They have an Act of Faith that gives them Relentless and Move Through Cover. That means they can move, shoot their bolters, and still assault. Yay? It's pretty good I guess, but the thing that makes the unit worth while is (again, we assume) Feel No Pain from the Sister Hospitaller. This is one resilient unit that can help us compensate for the loss of the 3++ from Spirit of the Martyrs.
Confessor/Preacher: Both of these guys let their squads reroll attacks on the charge. That's what they're for. The Confessor is somewhat of a combat beast with WS5 BS5, but depending on how much he costs he may not be worth it. I've heard that the Confessor is an HQ and the Preacher is Elites, though I'm really not sure. At any rate, what's important is their warband, er Battle Conclave.
Saint Celestine: Yes! She's got WS7 now, nothing bad happens to you when she dies, and she can return to life with d3 wounds and immediately move, shoot, and assault. There's nothing not to like about her, except maybe her cost, which we don't know yet...
Arch-Confessor Kyrinov: BARF! Everything about him is horrible. Especially his pug ugly model. Don't use him! Note however that he comes with a laud hailer and a simulacrum imperialis, and we don't know what those do yet, so maybe he's better than he looks at first glance.
Uriah Jacobus: Flat out amazing. He's not impressive in combat, and he carries a rather silly shotgun, and his model is ridiculous. However, he makes his squad re-roll attacks on the charge AND gives them +1 Attack. AND Feel No Pain. Yeah. Crusaders with 3++ and FNP is just rude, as are +1 Attack death cultists. Oh, and he lets your army reroll how many faith points it gets each turn. It's pretty hard to find a reason not to field this dude despite the silly shotgun.
Battle Conclave: This is the nerfed inquisitor warband for Sisters of Battle. It can contain arco-flagellants, which are horrible. You would never want to use them in a unit that can also contain death cult assassins. I mean, it's insane. Death cultists have the same Strength, the same Toughness, the same number of Wounds, only one less attack, and power weapons. Arcos have FNP compared to the death cultist 5++, but honestly that doesn't matter when then arcos can't kill anything. Crusaders are your bullet eater models in the battle conclave, death cultists are your damage dealers, and arco-flagellants are nice models to put in a display case somewhere. All in all, most armies will want at least one of these with a handful of crusaders and death cultists being lead by Jacobus.
Repentia: BARF! They have received significant buffs--Fleet, Feel No Pain, and Act of Faith that lets them make a single attack in combat attack even after they die, and 2 base attacks. But they're too slow to keep up with a mech army, and Rage means you can't control where they go, rather than staying behind a tank they're liable to run out in the open and get gunned down. If they can buy dedicated transports they will be AMAZING because transports negate Rage. But I seriously doubt they'll be able to do that.
Penitent Engines: Rumored to be Elites. IMO, if they cost 55 points or less (as they should, being AV 11 open topped), and if they really are Elites, they'll be great. 9 of these bad boys will have your assault needs taken care of. Rage sucks, but they're so freakishly strong that whatever they charge will probably get stomped. Of course, if they cost much more than 55 points, or if they're heavy support, then no thanks. Battle Conclaves for me.
Battle Sisters: I can't say much about these girls until we know their wargear options and squad size. Their Act of Faith is multi-purpose, letting them regroup regardless of restrictions (nice) and reroll 1's to hit in shooting or assault (crap).
Celestians: Not confirmed to be Troops, but their placement in the Bestiary suggests that they are... It makes sense too because our Elites section is stuffed (especially if Penitent Engines are in there) and we only have one other kind of Troops. If I had to predict, I'd say that Battle Sisters are cheaper and come in minimum squad size of 10, while Celestians are more expensive and come in minimum squad size of 5. This would let you spam 6 immolators full of Celestians as Troops, a tempting option--or it would be, if Immolators didn't lose their move-12"-and-fire rule. We'll have to reserve judgment on these girls until we see what slot they occupy and what exactly their wargear options are. And how much they cost, too.
Dominions: MANDATORY. You WILL take 3x units of Dominions. Why? Because they have Scouts now. Yeah. Oh, and their Act of Faith twin-links their shooting. And I hear they're cheap, too. This is exactly what the SoB have always needed. Don't even bother yourself with the other Fast Attack.
Seraphim: Assault 2 melta-pistols are cool. They can also fire both of their bolt pistols at once, which is nice. And their Act of Faith lets them reroll rolls to wound, which is cool when you cook a bunch of people with hand flamers. But they just can't compete with Dominions.
Exorcists: The rules for the Exorcist Launcher haven't been released, but rumor has it it's the same. The default choice. You probably want 3 of them.
Retributors: Heavy flamers. Heavy flamers! Heavy flamers!!! These girls can now (we assume) tote 4x heavy flamers, and their Act of Faith makes them Rending. That's powerful enough to challenge the Exorcist for a slot. On balance though, I don't think they cut it. SoB do not now and never had trouble destroying troops. Our challenge has always been range. And heavy flamer retributors don't help with that, and Exorcists do, so the Exorcist wins.
Now, Retributors can also grab heavy bolters and make those rending too. Rending heavy bolters will be able to glance land raiders, and they *do* help with our range problems. And rumor has it they're really cheap. My problem with heavy bolter retribs, however, is that they're never going to get a line of sight. Sisters of Battle are still a mechanized army, and your Retributors sitting in the back are going to be staring at a wall of friendly rhinos, compared to the Exorcist which can see over them. Not to mention that 12 heavy bolter shots = average 9 hits = average 1.5 rends. That's kinda sucky compared to the average 3.5 S8 AP 1 shots that the Exorcist throws down range. So unless there's some kind of Exorcist nerf, I think these chicks are staying in the case. At most, I'd take one unit of heavy flamer retributors and 2 exorcists instead of 3 exorcists.