Tough call. 2006-10 was a great period for Nintendo in general and probably their most profitable since the Wii and DS were complete juggernauts and they had more than enough software to back it up. 2013-14 I think are underrated since most will look back mostly on the mid-late 2000s, the 90's, and late 80's. During '13-'14, we had Pikmin 3, DK Tropical Freeze, Pkmn X, Y, and ORAS, Sm4sh, Bayonetta 1&2, Hyrule Warriors, FE: Awakening (outside Japan), Luigi's Mansion Dark Moon, A Link Between Worlds, Mario Kart 8, Kirby's Triple Deluxe, Capt. Toad's Treasure Tracker, and Mario 3D World, along with others I may have forgotten to mention.
Edit: Animal Crossing New Leaf (outside Japan) and Wind Waker HD also released in 2013. Japan also saw the release of Monster Hunter 4/Ultimate and Youkai Watch, two incredible hits in their own right, Dragon Quest VII remake, and Fatal Frame V around the period of '13-'14.