I liked the Sonic games (the good ones: the original through & Knuckles [and Spinball]), but I don't really liked the Mario platformers.

With one exception. Super Mario World is easily my favorite game in the entire genre, and I have played it to death. I've done all exit, all dragon coin runs multiple times. That game is as close to perfect as a platformer can get.

So, while I enjoyed more of the Sonic games overall, that single title pushes the Mario series to the top.