Objectivly I would say 2014, but subjetivly in 2014. I had only 2 games that rely interest me, MK8 and Hyrule Warriors, In 2013. I had Pikmin 3, WW HD and Mario 3D World, in 2015. I had Splatoon and Yoshi Woolly World, and in 2015. for now I will have Star Fox Zero, Zelda TP HD and Zelda U. So I would vote for 2013. and 2016. definitely could top that.

I'd say 2014.

2012 is in a distant fourth place. There were some good games at launch, but nothing exclusive that was groundbreaking or multiplatform that could single-handedly convince Wii owners to upgrade.

2013 was very barren until the second half of the year, save for that day we got both MH3U and LEGO City. It got better in the summer, with Pikmin 3 and W101, which ultimately were joined by Rayman Legends, Wind Waker HD, and SM3DW. But that still isn't many highlights, though one can still argue that 3D World is the best game on the platform.

2015 wasn't barren of releases, but too many of them were disappointing. Mario Party 10, Mario Tennis: Ultra Smash, Devil's Third, Rodea the Sky Soldier, and Animal Crossing: Amiibo Festival could have, and should have, been better game. Splatoon, Super Mario Maker, and XCX are great exclusives, but what other 2015 Wii U games will be fondly remembered?

2014 had some weak points, but was the best combination of quality and quantity. You want top tier Nintendo system sellers? Here's SSB4 and Mario Kart 8, the best Mario Kart in a while. You also want smaller Nintendo games? Here's DKC: Tropical Freeze, NES Remix, and Captain Toad. 3rd party collaborations? Try Hyrule Warriors and Bayonettta 2. Indie games? Here's Shovel Knight, Shantae, and Guacamelee. There were not as many notable 3rd party retail games as 2012 and 2013, but even then the only major losses were Call of Duty and Assassin's Creed.