It's New Leaf that led the way over the last six months, shipping 2.49 million worldwide and just over 2 million in the West; it came to Japan back in November 2012, before heading West in June. The cutesy sim's life-to-date figures are an impressive 6.35 million.
Meanwhile, despite being released at the end of March and just before the start of Nintendo's fiscal year, Dark Moon came in second with 1.91 million. More significantly, its life-to-date total is 3.13 million.
The remaining three all came in beneath the 2 million mark: the Japan-only Tomodachi Collection at 1.63 million, Dream Team at 1.37 million, and Country Returns 3D at 1.19 million. Together, the five 3DS games shipped 8.59 million units in those six months, contributing 31 percent of the system's total software shipments.
If you're not all statted-out by that, here's a final bit of info for you: New Leaf's figures would put it fourth on the handheld's all-time list, behind the plumber triforce of Super Mario 3D Land, Mario Kart 7, and New Super Mario Bros. 2. That's based on figures from March 2013, though, and the new Poke-games must be closing in after selling a crazy 4 million worldwide in just two days.