Yeah now it is easy since you will not have to worry about Animal Crossing or NSMB or Mario kart twice so my list is:
3DS:
In no order...
Kid Icarus Uprising
Super Mario 3D Land
Super Mario Kart 7
Resident Evil Revelation
Animal Crossing New Leaf
New Super Mario Bros 2
Super Smash Bros
Luigi Mansion 2
Pomen x/y
Monster Hunter 4
DS:
Mario and Luigi both games
The World Ends With You
Super Princess Peach (so cute)
Final Fantasy III/IV
Okamiden
Professor Layton - you pick one
Dragon Quest IX: Sentinels of the Starry Sky
Golden Sun: Dark Dawn
Pokemon Black/White
Switch!!!