Megaman - Elecman, because all I gotta do is stand on the blocks, shoot and jump when needed.
Megaman 2 - Bubble Man...
Megaman 3 - Either Needleman or Magnetman. Don't remember which.
Megaman 4 - Ring Man...
Megaman 5 - Charge Man...
Megaman 6 - Blizzard Man, because I like Blizzard Attack.
Megaman 7 - Burst Man, or if I did the trick to start with all 8 RMs, Turbo Man.
Megaman 8 - I don't remember.
Megaman 9 and 10 - I haven't played them, but I'd start with Hornet Man and Nitro Man respectively.
Megaman & Bass - Cold Man. His attack pattern is very simple, which makes it easy.