rebecca, you get her super early and she has end game potential as a ai companion. but almost all characters are good so you cant go wrong with any of them. and even if you do its easy to switch up and go with a different character so dont worry about it. :)

In early stages of game you don't need any characters to unlock. i mean I just use mc and she is destroying everything. i just leveled up her level, weapon, gun and skill and also she is at C1. and she is crazy powerful. For early stages of the game

Rebecca oneshots with a single E cast
insane for aoe content

I never actually aimed / farmed for any particular character - the mc will carry you far enough, so go for whichever character you enjoy the playstyle / theme of !! Obviously, later game you may want a healer / second dps for dungeons, but I’ve stuck with mc, and he’s carried me through everything so far.

TLDR - go for who you want. Mc is a good enough damage dealer.