I chose other for Sonic the Hedgehog. I don't much enjoy the current versions (though Rush is a step in the right direction), but I grew up on - and played the hell out of - the genesis ones. The series holds quite a bit of nostalgia for me.
Mario is an easy second. Each game in the series has captured my attention for many hours, and the spin-offs are quite good too.
In addition to Sonic, I'm disappointed to not see Kirby on that list. Not exactly my favorite series (generally too easy) but he's got more games than a few of those franchises. And spin-offs to boot.