~Survey~

ice pixie
why ? because its very good in pvp not like chaos pip the opponent can be countered but pixie cant so you can skill/grab ^_^

GP dungeon: sidtri
GP pvp: chaos pip, pip(gorge of oath)
Mission reward dungeon: myurin(defensive play), LittleKaze
Mission reward pvp: myurin(defensive play though I'm not fond of that style)
Cash dungeon: gorgon
Cash pvp: ice pixie(freeze), gorgon(stunlock)
Gacha/Limited dungeon: DMG MK-III, pierrot(only if bombs explode in air)
Gacha/Limited pvp: nerisa(damage, its air launch is good at gorge), grifis or romeo(confuse), imp(long range haste effect), kerby(stunlock)

remember each of us have different play style