Mario Vs. Sonic.

[Sunlight]

I'd say it's hard to compare the games with each other, but going with the actual characters, I'd say the big difference is that Mario never really was much of a character. He never (or atleast seldom) had any dialouge, and he served more as the players avatar to interact with the other characters that actually, well, had different personalities.
Sonic on the other hand started talking basically as soon as technology allowed him to and thus developed his own personality...
...
A personality that made me vote Mario.