Some of you guys have ridiculous hours on some games O.O...
From the top of my head, LoZ: Ocarina of Time 3D is the number one. I got the 3DS on OoT's release day. Mario Kart 7 has been the fastest climber though, basically if I play it one more time it'll be at number 2, likely to be number 1 some day.
Ocarina of Time 3D: 80hrs
Resident Evil: Revelations: 30hrs
Mario Kart 7: 30hrs
Super Mario 3D Land: 25hrs
Luigi's Mansion: 20hrs