User blog comment:SuperAurelius/Who should be my UoC?/@comment-26347196-20161026234821

I'll probably give you a list from most favored to least (imo), and their additional buffs apart from their obvious ones (which is mitigation or spark buff - I'll include everything in terms of BB fill, cause there's a lot). And I'll include most of them bc I don't know your roster of units (which is fine)


 * For mitigation:
 * Elimo -Def/Rec boost, HP recovery when attacked, barrier, and some bunch more negation (critical, parameter drop, elemental, ailments) according to what SP you want (Her OE is not released yet but soon)
 * Krantz - mitigator (2 turns on SP), BC/HC drop, heal, cure ailments (can spend SP for better flexibility), adds Light/Dark element, the only unit with potential 4-turn UBB mitigation on SP.
 * Stein - mitigator (2 turns on SP), ailments removal, HP recovery when attacked, barrier, and you can tweak between Medic Stein or Revenge Stein on SP options.


 * For BB-gauge up buff:
 * Zelnite: BC/HC drop, BB fill rate, BB when attacked, insta-BB fill, OD fill rate, spark blanket, normal nuke strategy on UBB, an overall farmer himself.
 * Felice - BB and HP fill on spark, spark blanket herself, BB fill when attacked.
 * Rengaku: BC/HC drop, insta-BB fill, insta- OD fill on SP, BB fill rate, and other misc stuff like Atk conversion buff and critical spark


 * For Spark:
 * Elza: status infliction, insta-BB fill on BB, BBoT and HoT on SBB, Def ignore, spark blanket, and you can add critical spark or BB fill on spark from her SP options (not recommended tbh).
 * Daze: Parameter boost, BB fill rate, and some critical department on her SP.
 * Vern: P much a pro-sparker with additional spark vul and crit spark, added some elements to attacks, and you can add BB fill on spark buff from her SP.
 * Izuna: I'd say her strong point is Arena, so you might wanna consider that.