Wooohooo! Contest! Thanks for this, goomba. Now I get to possibly mooch of your free stuff. Or someone else will... >_>;
Anyway, favorite Mario game.... I'll say Super Mario RPG. I like RPGs (especially ones made by Square) and I like Mario. It's a great fit. But if you mean traditional Mario game, I'll go with Super Mario World. It's a lot easier than SMB3 and the real SMB2 but I do love easy games much more. Which is strange, because many times I play games for the challenge...
As for favorite enemy, the Chargin Chucks! Those guys are awesome! They'll tackle you, throw baseballs at you.... do some sort of cheerleader-esque jump at you.