2014 would win due to stronger back-catalog (Super Mario 3D World, Pikmin 3, Wind Waker, etc) and many new highly anticipated games covering a wider genre of titles like DKC Tropical Freeze, Mario Kart 8, Smash Bros U, Fire Emblem X Shin Megami, Monolith's X, Bayonetta 2, etc
The value proposition should also continue to improve with lower entry cost, and pack-in games (Super Mario 3D included would be better than New Mario included, etc)
The one risk is that 3rd party support will get weaker, and some really strong titles from 3rd parties will be going to PS4 and XBO without going to Wii U (like Destiny, Elder Scrolls Online, Witcher 3, etc).
The way I see it, in 2013, the Wii U was the go-to console for Platformer gaming fans with Rayman Legends, Luigi U, and Super Mario 3D World. In 2014, the fans for kart racing, fighting, rpg/action, strategy, and platforming will all get more/better reasons for adopting the Wii U.