I'd say go Nicole if you want a bot that's usable. Melfi-chan is pure cuteness, that's about it. Maybe they'll buff her... but I kinda doubt it with how the gm's work. They'll most likely buff Elisa and reg Melfi, and leave the poor chibi in a cardboard box in the rain (insert sad moe mental image).
Nicole does have a good starting flight. I suggest not using it if you intend to tune her. She can get float dash, and this can be a nasty combo with her scepter. Though, with dead eye out you become a sitting duck (float dash lasts <1 sec with him out).
