Celestians are your veteran sisters. They are the same as old-school Space Marine veterans, back before they were split into Vanguard and Sternguard variants, in the Sister of Battle list. They have the same statistics as a normal Battle Sister, except with +1 Attack and +1 Leadership. However, their Act of Faith is horrendously bad, leaving them a rather lacklustre unit on the tabletop. For one turn, they get the Furious Charge skill. In my opinion, this is a terrible Act of Faith. If they charge, they become Strength 4 for a single turn which means that they may not horribly mess up in melee combat for that phase. They do, however, remain Initiative 3, so some of your elite Battle Sisters will probably be killed before they can do anything. From a fluff perspective, they are a wonderful addition to any army and I personally take one unit in most scenarios; they are, however, competitively a waste of points that could be spent better elsewhere. Their effectiveness at range is decent, however they shoot just as well as their non-elite Sisters whilst costing more. They can take identical upgrades as Battle Sister squads, being a special weapon, a heavy or special weapon, a Simulacrum Imperialis and the Celestian Superior could take melta bombs, Melee Weapons and Ranged Weapons from the armoury. They may take a Dedicated Transport of either a Rhino, Immolator or Repressor which, in my opinion, is largely worth it due to their very small points and potential to get more heavy weapons mounted on vehicles. I’m not a huge fan of the Repressor as it feels less “Adepta Sororitas” than the other option, but it’s a solid Dedicated Transport.
Sisters Repentia are an interesting choice. On one hand they can deal insane amounts of damage in melee, however the question is whether or not they will ever get there. They are Toughness 3 and only have a 6++ Invulnerable Save from Shield of Faith. They still have Rage, Fearless and Fleet, their Act of Faith gives them 3+ Feel No Pain which makes them incredibly durable for one Assault phase and they all still wield eviscerators. They may now take their own Dedicated Transport which you will always do for this squad. If you do not put them in a Rhino, they will be wiped out in the first or second turn due to having only Toughness 3 and a 6++ Invulnerable Save; they make Howling Banshees look durable, which should never, ever happen. For 14 points per model, they can not withstand any fire power from any unit unless driven into the opponents face using an equally suicidal Rhino. Taking this squad will likely give your opponent First Blood, so it should be seriously considered when thinking about taking this unit. However, it has been brought to my attention that Repentia can be an incredible titan-killer unit. With a high number of attacks hitting at the same time as stomp attacks, you’ll likely be able to carve open the likes of an Imperial Knight at the same time that it steps all over your unit. Repentia will rarely survive a game, but their success hinges on how much they can take down before they go down themselves.