I can only speak for the Vita, but wow, have I really been impressed with the hardware. The screen is beautiful, the multi-touch is excellent, and the dual analog sticks really do make a big difference with gaming. It's just a really awesome device.
Honestly, if you have a PS3, then I suggest you go for a Vita, mostly because of PS+. I bought my Vita on Black Friday with three months of PS+ included and so far I haven't bought anything for it because I've been playing the Instant Game Collection selections. Mainly Gravity Rush, Mutant Blobs, and Final Fantasy Tactics, but Wipeout and Uncharted are up next. Of course, since you get the PS3 games as well, I've also been playing those. PS+ wasn't something I was really interesting before but now I'm a believer.
Still, as with any system, it's about the games you want to play. I bought my Vita mainly for Gravity Rush, Persona 4: Golden, and Soul Sacrifice (which looks amazing). Tearaway and Killzone Mercenaries were also factors.
