I think, as a whole, the games are better-made and offer a wider experience of gameplay. I'm certainly not close-minded about Sonic, but given the choice between the two, I'd take Mario any day.
hmm..SNES/ Genesis era Id say Sonic, N64 and beyond though Id say Mario. Colors and Generations are fun, but overall Mario just transitioned alot better into 3d imo. I still play them both so it doesnt really matter I guess lol.
While I considered myself more of a Mario fan (due to his overall quality), I love Sonic 2 and Sonic Generations HD more than all of Mario's games. For the most part though, it more or less depends.
I just started to play Sonic a few days back (Colours) It seemed challenging And I was raised with Nintendo systems, so Mario has been my preference However, I'm all up to try more Sonic games