honestly, only get the 3ds if you really like nintendo games like mario and zelda.
you can literally go through every other feature of the 3ds and it is better on the ps vita.
a way better browser
much better music players
better video players
a more sensitive touch screen
a better looking screen (OLED, high res, and much bigger)
two analogue sticks (the 3ds has one)
ps3 graphics (3ds has wii)
back touch pad for L2 and R2 (3ds has nothing)
cloud saves (start game on ps3, save, continue on vita if you have to travel - awesome)
cross platform online (play online with people on ps3)
tons of fantastic games - my faves -
Final Fantasy 10
Monster Hunter Portable 3 HD
metal gear solid 2 + 3 ( as well as new project from metal gear solid creator)
Uncharted Golden Abyss
Call of Duty
Ruin (looks beast)
Marvel vs Capcom 3
if you are really into nintendo games like mario, pokemon, zelda, animal crossing, and that stuff, then get the 3ds.
but otherwise, get the vita, because it does everything other than nintendo games better than the 3ds. hands down.
all vita games - http://en.wikipedia.org/wiki/List_of_PlayStation_Vita_games
hope this helps!
big fan of DS, did a lot of research on both vita and 3ds.