IMO, the Wii U has a much better library now and lined up. The thing is though, I only care about the first party games. I don't really have much need for any third party games, since they would be multiplatform and I would just get them on PC.
The PS4 and XBOne have nothing to offer to me right now. Their best games are probably Battlefield 4 and Assassin's Creed, which is would just buy on the PC. Their best upcoming games are probably Watchdog or something similar, which I would just buy on PC. I think that will change in the future with the PS4 once the inevitable console-only Japanese games come out, but I doubt I'll ever get an XBOne unless a surprise comes in the future.
I realize I'm different than most. PC is my primary gaming platform, which takes the place of a PS4 or XBone of a 'normal' gamer. That said, I still think the Wii U is a great companion console. It offers another sphere or take on games, where as PS4+XBone would have too much overlap with each other. This is especially true if you care about couch co-op, or are tired of the FPS/3rdPS inundation.
I think the Wii U's main problem is marketing. Where are the "Would U like to play?" commercials, or some equivalent? Hopefully they can get that figured out. Although it doesn't matter too much to me, since I basically buy only first part games and that would get made regardless.
The most important thing is to remember that the Wii U doesn't have to sell more than the PS4 or XBone to be successful. It isn't in the same race or targeting the same market necessarily. It just has to sell enough + enough games to make Nintendo a healthy profit, which it has failed to do thus far.