Nintendo's latest financial results (April -- September 2013) list five new additions to their million-seller list. These 3DS games all did well this summer, but Animal Crossing: New Leaf did especially well. Joining it are Luigi's Mansion: Dark Moon, Mario & Luigi: Dream Team, Donkey Kong Country Returns 3D, and the Japan-only Tomodachi Collection.
New Leaf moved 2.49 million copies in the past six months, with 2.01 million of those being sold in the west. On the opposite site, all of Tomodachi Collection's 1.63 million units were sold in Japan. And I think if it were released in the west, that number wouldn't change much.
Now, when it comes to lifetime totals, New Leaf's 6.35 million unit total towers over the others. That won't last long with Pokemon X and Y hot on its heels.