I already have a 3DS, and im definatey getting Vita too, possibly 1 or 2 months after launch. I liked and played my PSP much more than i did on my DS, so i do expect Vita to be better for me.
Also, if you want to play PSP games, i seriously recommend you get an old PSP model so you dont have to rely on PSN availability. Trust me, there are a lof of great PSP games missing on PSN. ANd you can get a PSP dirty cheap now anyway.
HGiles: I have a 3DS and I love it. The battery life is definitely short, but it's not that bad, especially if you leave the wireless off. I usually get 5-ish hours without needing to plug in.
The 3DS-specific games lineup isn't great yet, but it's getting better.
Chevve: So far the games I'm interested in:
-Super Mario 3D Land
-Mario Kart 7
-Sonic Generations
-Nano Assault
-Animal Crossing
-The inevitable Pokemon game
-Tales of the Abyss
-Heroes of Ruin
-Monster Hunter
Sadly most aren't out yet, or even have a release date. D:
I would take Sonic Generations off your list, if i were you. I was expecting a lot from it, and i catually wanted to buy it, until i read some user reviews and found out that the game is nothing compared to its console counterparts. Everyone complained that level design is dumb and the game lenght is about 1 or 2 hours. I would never ever pay 40 dollars for a game thats 2 hours short.