This is a tough one, personaly i think they're both equal, but gamewise i really prefer Mario to Sonic.

I like Sonic's games but recently i think they've been a bit too "serious" regarding the storyline's which are becoming increasingly dark and angsty somewhat, plus they like to force you into finishing it (or at least Heroes and onwards did, SA2B had Chao and other fun stuff), while the Mario games on the other hand are all about doing pretty much whatever you want, they're very laid back and let YOU decide when you want to do stuff. Super Paper Mario is a decent example of this, aside from the main storyline you can pretty much do what you want, and its not like there's little to do either, there's the recipe's, catch cards, maps, its all there just waiting for you to explore them, and when you dont feel like doing something that feels like a mission, there's the good old mini-games for you to screw around with (which use the Wiimote's abilities quite effectively might i add). It is just lovely and i really think a lot of Sonic games lack this.

I am a fan of both but i hate how stuck up pure Sonic fans always rant on about how Mario is just a fat useless plumber who rescues some dumb princess who gets kidnapped by a turtle. You may hate Mario but in the end his games are the most enjoyable, maybe even more enjoyable than any other games series.

I love them both because i pretty much grew up with both, but overall i much prefer the Mario games to the Sonic games, both spin-off's and staring roles.