Crono and Robo are total locks IMO. You need healing, Luminaire is super dumb for damage, Life is nice to have, and they hit hard as hell. Afterwards it depends. If you can swing physical damage Ayla is the way to go for sure, she's just incredible in all fronts except utility - otherwise Lucca is the better choice because she brings a nice, always useful buff to the table, insanely strong techs, and elemental variety.
--
Placeholder anti-capslock sig.