Blade is actually one of the best characters in the game. His moves are powerful, and for some reason, he has the Leadership passive which is invaluable. Elektra is really good as a support character, you just have to know how to level her up (her and Blade are regular mainstays in my party actually).
Colossus absolutely sucks. His powers don't deal enough damage. I know I could open up the powerstyle and change that, but I don't care to. I did however, make him a bruiser character. He needs to be a heavy hitter. A boost should reduce the damage for him, not having insane amount of body (hp).
Moon Knight is a Gambit with a few tweaks. I liked Gambit, but have no idea who Moon Knight is. I don't think he's iconic enough to care about.
So my vote? Rogue. She solid, versatile, and has big boobs.