As far as healers go:

SCH > AST >= WHM

SCH:
Scholar is always going to be the most obnoxious to try and deal with due to the lolfairy that can simply prevent you from dying almost always, as well as the fact that they bring a shit ton of emergency buttons that can save the day. The problem is that their PvP skills suck, Aura Blast is useless as shit.

AST:
Astrologian actually has found a nice niche in PvP, and honestly, this is where Noct Sect actually becomes useful. The get a nice instant cooldown button and instant cast adloquiums, as well as light speed that pretty much ensures that they can sustain themselves or any party with relative ease due to no wait timer on casting spells. Plus, enhanced Balance on someone with battle fever is insane. Retrogradation is also pretty insane, as it removes buffs on enemies, removes debuffs on party members, heals, and damages at the same time.

WHM:
White Mage is still very much viable, but they lack good cooldowns to save themselves in dire situations. Tetra is nice but it's honestly the only thing they have, as Benediction has a ridiculous cooldown that makes it unreliable. Assize + Asylum are nice but you move around too much in PvP for them to be too entirely useful. They do have Sacred Prism though, which can honestly render any melee useless for a good while, as it negates 40% of all melee damage.