PS VITA - 250$. Most of the games for VITA are ports. Sony is more or less turning the Vita into a controller for PS4 since they know it can't do as well as the PSP did. Not to mention stiff competition from 3DS.
3DS - 170$ or 200$ for XL. Well what can I say large games are already out with more on the way (Smash, Pokemon , Mario and Luigi Dream Team, Zelda, I'll stop there)
If you want my opinion, I think if you really want Vita wait until E3 and see what happens. Because as it stands right now a lot of developers are skipping the Vita (Monster Hunter 3 from Capcom decided to release only for 3DS).
Personally I'd go with 3DS. Why? Because it has a future with over 30m sales without something as big as Pokemon even out, it is definitely going to have an amazing year.
Vita on the other hand isn't getting much attention from Sony and with 5m sales, it makes you wonder if this is even a Handheld anymore with what Sony is planning.