The Wii U is a beefed up Wii, which was a beefed up Game Cube, and can play games from 3 generations with some tweaks.
The Xbox One is a beefed up Xbox 360, which was a beefed up Xbox, and can play games from 3 generations with some tweaks.
One got a weird gimmick at launch, that faded out quickly, the other one too. There are a handful of interesting games in one, same as the other one, which all can be played on their successor in a superior version.
Hard to choose