That last entry is a boss compilation. It's also probably a compilation in the Giant battle section too. I can't beat Bowser X

Animal Crossing New Leaf, about 85 hours so far.
Lol, 2nd is Swapnote/Letterbox at 56 hours, apparently.
Mario Kart then with almost 50 hours.

My least played is Donkey Kong Jr with 1 minute at #57. xD

Mario tennis open. 150 h
i love that game.i must be one of the few

Fire Emblem Awakening, I should be nearing 140h

Ah, it's nice to no longer be a lurker.
Anywho, my list:

1. The Legend of Zelda: Ocarina of Time 3D - 36:22
2. Super Mario 3D Land - 35:02
3. Kid Icarus: Uprising - 33:04
4. Mario Kart 7 - 32:24
5. Resident Evil: Revelations - 26:35
6. Pokémon Black Version 2 - 25:28
7. Animal Crossing: New Leaf - 25:12
8. New Super Mario Bros. 2 - 24:29
9. Fire Emblem: Awakening - 15:55
10. Luigi's Mansion 2 - 15:54
11. Star Fox 64 3D - 12:40
12. LEGO Star Wars 3: The Clone Wars - 11:42
13. Dillon's Rolling Western - 10:22

Quite bad, really ;D

Mario kart 7 by far

Actually, my most played game on the 3DS is an ambassador game. Fire Emblem: The Sacred Stones to be exact. Played it for 300+ hours. Awakening currently ranks second with about 250 hours I think (but I'm a huge FE fan so this should be expected). I played alot of Pokémon Black 2 / White 2 on the System as well, as those games came out after I owned one, and Mario & Luigi: Dream Team Bros. is currently shaping up to become my most played 3DS game if you don't include Fire Emblem. At the moment, I am playing Project X Zone, which will likely end up with >30 hours of playtime. Some other games I play(ed) extensively include Kid Icarus: Uprising, Theatrythm Final Fantasy, Pokémon Mystery Dungeon: Gates To Infinity, Dead Or Alive: Dimensions and Sonic Generations. Plus some DS games I have gotten since then, like Advance Wars (both titles), Fire Emblem (both titles obviously), Pokémon Conquest and the aforementioned B2/W2.

It is because for some the 3DS is their main game console, it doesn't matter that it is portable. And that is my case, i got the 3DS on christmas 2011 and since than i play it the most, last year i only played skyward sword and xenoblade on Wii, most of the games that i wanted to play on the ps3 i already played and i need to buy a new pc for my gaming pc fix, my pc is six years old and it wasn't a top pc at the time.

So it is 3DS all around.

OP: i will be posting my numbers soon.

101 hours on Fire Emblem: Awakening without the paid DLC, 55 and counting on Animal Crossing. Behind that are Ocarina 3D and Kart 7 on 40 something, and Monster Hunter on 30, which will hopefully get more playtime as my friends have just bought it.

Probably Sticker Star. Played it for a solid 26-27 hours or so. Longer than OoT, and it's the only 3DS game I've bought with any real length, if you don't count 3D Land since it's so short, or MK 7, which is just multiplayer.

Of course, I'm going to GameStop today after work to pick up my M&L pre-order, so the Sticker Star record will soon be beaten on my 3DS for longest playtime.