Who's better - Sonic or Mario?

I was a huge Sega fan from the Genesis days so originally I was a big time Sonic fan. These days I prefer Mario, mainly because Mario games tend to always be enjoyable whereas Sonic games are getting progressively worse. I mean now you can even have them go head to head in that Mario and Sonic olympic games or in Brawl for Wii.. but while I like both, Mario seems to be able to withstand the test of time far better than Sonic.