Sonic wouldn't fit cause his ability is running fast and wild, while in smash bros it's more like hand to hand combat. Sonic doesn't do that. He runs and rolls.
I kinda understand the sonic hate today, due to how they try to street cred him and all, but back in the 16bit era he ruled big time. Sonic 1-3 are still awesome games.
Megaman on the other hand is a lot like samus with his abilities.