I'd take Ba'gunar honestly. There's several enemies that are weak to Lightning in important ways and Paralyzing Blade is reliable (even after going from 100% to 80% in the patch). He also creates Anti-Shadow Capsules which is handy. Followed by Sampui for his weapon triangle versatility and eventually learning Control Time.
Jaguna is trash and Burbaba is a counterattack-type adventurer, which might have a niche but I found it pretty worthless. If you need the enemy to attack you to get your skills to work, it's not reliable (and it only triggers off enemy pincers and any enemy that matters isn't going to be attacking you with Pincers). Also, I think O'pari is pretty lackluster since most of his skills are filled with low damage Fire Arrows but having a fire element type attacker wouldn't be bad to have eventually. Elements are more dramatic then weapon triangle so there's no worry about having two archers unless the stage preview says it's full of swords.
... I dunno how one would get by without a healer, you can't dodge all damage, so definitely take your C-rank generic until you can replace her proper.
