If it were to be set via skills, then you would have to say
Sonic would win athletics
Tails would win any jumping contest
Bowser would win hammer throw, shot put etc
Mario is pretty chubby and so i doubt his really olympic material lol
I've got it on my list, but first I need Call of Duty 4 on 360 and maybe Assassin's Creed...oh and Gran Turismo 5 Prologue...
Bah! Too many games this Christmas.
Tails and Luigi will make a pact after being fed up from being left out of the limelight (and royalties) for so long and they will sabotage the games, then get found out.
Eventually all 4 will be disqualified and Yoshi will win.