I've really been loving my 3DS XL since I got it last year. If you can't go without the Mario/Pokemon/Animal Crossing/Zelda games I would highly recommend a 3DS. Personally I've found much more on the 3DS than just those franchises; Ghost Recon, Fire Emblem, Theatrhythm and Shin Megami to name a few.
Sorry I can't speak to a Vita as I don't have one but I think the 3DS is a great investment and as far as I see it is only getting better. Good luck with which ever console you end up going with.