I bought myself a 3DS when it was $150 at Gamestop. Bought a Nyko power pack and 16 GB memory card for another $27. The 3DS works so much better as a MOBILE gaming platform that the Vita just misses completely. Even the games that have the Circle Pad Pro work great WITHOUT the accessory! Both MGS and RE play wonderfully and I have a blast playing on the go. When Sony said the Vita will be more about mobile gaming, I though GREAT! Lets see it! Then it just turned out to be a PSP with an addition joystick and ended up being bigger, wider, AND FATTER!
The point isn't to get the PS Vita BIGGER! The Vita has to compete with smart phones and making it bigger only makes smart phones (and the 3DS) look like the more pocketable option. Sure, the PS Vita (with both stock batteries) is technically better in every way than the 3DS. BUT, once I replaced the battery of my 3DS with the Nyko battery, I easily have 8-10 hours of play per charge. Not only that, but I bought a 16 GB memory card for $17 (the 3DS comes with a 2 GB out of the box) while the PS Vita has a 16 GB memory card you HAVE to buy for $60. That's well over 3 times the price! And with a battery I cannot replace with a bigger one (because of the touch screen back!) even though the PSP COULD have the battery replaced. Not only all of those reasons, but to stop playing, I just close the clam shell and pocket the 3DS... takes two seconds (if that).
So my suggestion? Go with the 3DS for sure. It currently has more games (with more being developed for it since some companies switched development), you can get a better battery for it (and much cheaper memory), it's easier to use as a mobile gaming platform, the virtual console lets you keep your classics, AND it will have Pokemon on it soon (
announcement hopefully soon).