Evolve them as soon as possible!
Karrablast and Shelmet both are super bad. Also, Escavalier and Accelgor get decent moves early on.
Now lets see the pros and cons of each Pokemon.
Really good attack
Good defense and special defense
Has access to good stab physical moves
Really good speed
Good special attack
Has access to good special moves
I would go with Accelgor because it will probably out speed the opposing Pokemon and kill it in one turn.