I think the title said it all.  Feel free to explain why as well.

For reference, according to VGChartz:

2012: 2,247,216

2013: 3,232,667

My guess: 2015.  I say this because it will gain momentum in 2014, which won't reach its fullest until the end of the year (mainly from Smash), and that will give the system a strong status and probably more noteworthy games.  I think yearly sales of the Wii U will be a smooth bell curve.

2015.

2013. As was shown in the NPD thread is tracking lower than the gamecube and the dreamcast. It may struggle to 10 million but not much more

2013 because YOY was recently revealed to be LOWER than last year. So looks like it's possible it will sell less 2014 than it did 2013.

There is no way it will peak in 2015. It will decline rapidly after 2014.

It looks like 2014 if barely ...

2014, maybe 2015, depends if it gains momentum at the end of this year or else the spikes that software could bring this year, and maybe a pricecut, will be the highest point

2014, over 5 million.

so do you think with Mario Kart (bundle) and Smash, it will sell less than 3,5mil this year? ok

2015 since 2014 will establish a much stronger audience and peak at 2015. By the end of 2015, Nintendo will possibly have released huge 1st Party games like Zelda U and Metroid.

2015 for the same reasons you said. Maybe 2016, but i dont think Nintendo has anything crazy coming out after 2015, so i will stick with 2015.