It depends. If you don't own a PS3 and, to a lesser extent, the 360, and don't plan on getting one or the other, then the Vita.
If you own a PS3 or 360, then get a 3DS XL. Don't even think of getting the regular 3DS.
The Vita has better games if not for the fact that just about all of them are playable on the consoles. However when it comes to exclusives, the 3DS wins. The Vita has some good ones, and is catching up, especially with this month having Ys and Tearaway as two more possibly good ones, but the 3DS overall has more.
*edit*
Multiconsole games between 3DS and Vita are superior though, so if you're thinking of a few of the 3DS/Vita multiconsole games and you're eventually getting both, then wait until you get a Vita to get those games.
Don't let people fool you though. While the 3DS has more good exclusives, it's due to the fact that they have more in general. The Vita is behind, but it's not too far behind the 3DS when it comes to exclusives worth owning.
