I have a 3DS XL, but no Wii U. I'm waiting for a price cut and some good games to be released before I purchase it. It's not a question of if I buy a Wii U, but when I buy a Wii U.
As for the 3DS, I adore it. I lost interest with most console games last generation and grew to love the games on the DS and PSP. I love the convenience factor of grabbing the 3DS off your coffee table, flipping it open, and immediately playing a game. Want to stop playing? Close the lid and pick it up tomorrow. I absolutely love that. And the games are so much more innovative. Portable games have much lower production costs, so I think developers are willing to take more chances with quirky and unique ideas. Something like Etrian Odyssey, Locoroco, Patapon, Phoenix Wright, Professor Layton, or Theatrhythm Final Fantasy would never be able to justify a console-sized budget.
The only thing I dislike about the 3DS XL is how large and thick it is. Sure, the huge screen is very nice, but the system is about the same size as a Game Gear. It's not comfortable to hold for long periods of time and it's almost painful to walk around with that thing in your jeans pocket. The Vita is a much more reasonable size -- if only it had games.