Depends on what you grew up with, I feel. Every gamer who was young at the time must have some kind of primal image of either of these guys imprinted into their long term memory.
Nothing was as magical Mario All Stars if you were at the right age when you first played it. The art for Mario's games has a quality that's indescribably magical. It feels iconic, it feels like they got everything right.
I tried Sonic way way later, and it just didn't click with me. I think the games are OK, but they feel less authentic than Mario. Like one of those rip off SNES platformers they'd make for movies and random characters, like Zool.