Honestly both the 3ds and the Vita are collecting dust at the moment on my shelves. The real problem with them is that the full sized consoles are directly competing with the handheld ones. Every time they release a spin off on the Vita one has to ask is it worth buying the spin off, or the actual game that it is spinning off from? So far reviews point to buying the original game that the spin off is based off of and my own experiences seem to be in agreement.
Going to say it outright though, the Vita is by far a MUCH better handheld design than the 3ds. Two thumbsticks does make a lot of difference and the Vita is just a lot more ergonomic. The console really could have lived without the rear touch pad, though.
My recommendation for games on the Vita is Uncharted, Gravity Rush, and Persona 4 the Golden. However, just be mindful that Gravity Rush does have some interesting control problems for timed events and the costumes are pretty much all DLC...