The Elites section of the old White Dwarf codex was a little lacking. Celestians just could not justify their points cost and Repentia went from being a massive joke to a suicide squad. Past these two squads, that is all we used to have for Elites. First, I shall talk about Celestians.
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. In my opinion, they have become a lot worse. True, they have dropped to 14 points, but their Act of Faith is horrendously bad. Now, for one turn, they get the Furious Charge skill. In my opinion, this is a terrible Act of Faith. They, if they charge, 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 or Immolator which, in my opinion, is largely worth it due to their very small points and potential to get more heavy weapons mounted on vehicles. A lot of people take hordes, so a lot of people gear their armies against lots of infantry. When you show up with a load of tanks, it forces your opponent to think on their feet and puts you in a comfortable position. This is entirely hypothetical as I have yet to field this and have not played enough games to make accurate guesses as to the current meta. Also, the meta in one place is likely to be different to the meta in the other, so this could be a terrible strategy for some as much as it would be amazing for others.
Finally, because the Adepta Sororitas codex only contains two Elites choices, we come to the Sisters Repentia. Repentia have, in my opinion, been nerfed. The largest punch to the face is that they have lost their Feel No Pain special rule, which made them not just die quite as much, now only possessing a 6+ invulnerable save due to 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 firepower 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.
All in all, I like taking a squad of Celestians for fluff reasons, but otherwise I tend to stay away from Elites in general. They are expensive and largely inefficient for their points cost, but very apt for most fluff based armies. Competitively, they are rather terrible and pale in comparison to units later on in the codex, but that is for another article.
Keep Calm and Purge Heretics. Preferably with plenty of flamers.