Wow, a surprising amount of bitterness in this thread...
And for the people saying the Vita has a better library: Are you sure? The Vita has one game above 90 on Metacritic, whilst the 3DS has five. I know Metacritic isn't a barometer mostly, but the games I have enjoyed on the Vita are Persona 4 and Gravity Rush. I liked Little Kings Story, but the Wii version was better.
However, those games do not stand up against the likes of Zelda, Mario, Fire Emblem, Luigis Mansion, Resident Evil and others. Comparing the future lineup as well, the 3DS wins. Soul Sacrifice is the only real game I can see being worthwhile in the near future, and this is not a huge system seller sadly. But the 3DS has the recently released games mentioned above, as well as Pokemon, Mario and Luigi, Monster Hunter 4, Animal Crossing and others which I've forgotten about, launching within 6 months. These are all games which will likely sell a million units before the year is up.
You can argue quality in different ways, I get that, and the 3DS may be for you. But on almost every way you look at it, the 3DS wins out. The only way it doesn't is if you really don't like Nintendo games, and if such, why get a 3DS in the first place? Both systems are great systems and I love them both. But the Vita deserves better support, and this is what is giving the 3DS its lead. Even last year when game releases were few, the Vita couldn't capitalise. If it couldn't then, then it has no realistic chance now.
I don't mean to come off as offensive, but that's my view. However, the Vita is the better product from a build perspective.