2014 thanks to MK8 and Smash Bros 4, which is kinda sad because 2015 seems to be the year with the higher number of good games!

It should sell more in 2015 as it's still trending up in it's lifecycle, same for pretty much every console ever. After that you level off and by 2017/2018, suddenly the ninth generation seems so close and the sales go down.

2014.

For it to sale more it would need to take consumers away from the others. Especially the PS4 and that's just not gonna happen. Also U is close to exhausting the supply of ninty fans to sale to.

Another reason is it will be facing an onslaught from PS4 and its games, PS4 with all the 3rd parties and exclusives and indies will be a far greater sales beast then its been already. In no realistic scenario is what wiiu has enough to compete with that.  Add potential morpheus and PSNOw to PS4s aresenal.

U had a good chance to build up a relevant lead that would get it support and chance to up sales later. But its a bit late for that. So 2014 will be its potential highest year. Unless it can be some how marketed as a awesome secondary console to the PS4. A Wii60 type deal.

2014. Now they'll go down again, and maybe they will recover a bit in 2016.

2015.
because don't have the departure of 2014, and because coming Zelda, X, Star Fox, more, ecc...
For me even in 2016 will sell more.

I think 2015>2016>2014>2017>2013>2018>2012>2019>2020

Obviously, 2015 makes 2014 look like a joke.

2014:

Donkey Kong Country Tropical Freeze

Mario Kart 8

Wii Sports Club

Hyrule Warriors

Bayonetta 2

Sonic Boom

Mario Party 10

Captain Toad Treasure Tracker

Super Smash Bros 4

2015:

Legend of Zelda U

Kirby Rainbow Curse

Splatoon

Xenoblade Chronicles X

Devil's Third

Fatal Frame V

Star Fox U

Mario Maker

Mario vs Donkey Kong

Yoshi's Wooly World

It'll be pretty close IMO.

2014, mainly because of MK8's sales numbers as well as Smash 4.

I can't see the WiiU selling better in 2015 than in 2014, considering how MK8 and SSB release in 2014 and 3DW released at the end of 2014. This means that the most succesful Nintendo IPs, excluding Zelda, will be already available on the WiiU by the end of 2014.
If Zelda in 2015 is strong enough, it can allow the WiiU to sell more or less like in 2014. If it's not epic, though, sales in 2015 will be below those in 2014.

This year they had slow start only started to pick up after Mario Kart 8. They have Hyrule warriors in September (October for Japan), Bayonette and Smash Bros to finish off the year. Watch Dogs this fall but I think it would have help if it launched with the other versions.
2015. We have Splatoon (If it's priced right), Star Fox, Xeonblade, Zelda U those are just the "confimed" ones. I believe there will be a New Open World Mario game, Metriod, Zelda Remake and a Price Cut.

2015 my guess.