These days for me, Lara. I do take Mario games for granted, but his character could be almost anyone else and it'd still work.
Lara is Tomb Raider. She defines her early games. In Mario games, i don't usually even choose him if there's a choice.
I usually pop in Tomb Raider like once a year for a few hours fun.
Throw in other characters like Sonic, hulk, Spiderman or Luke Skywalker, and my answer may change.
Warning: Sometimes biased
http://i.imgur.com/V0x5fw8.jpg http://i.imgur.com/IOovUge.gif http://i.imgur.com/zw7bqPH.jpg