Vita is a no go ... no teenager/adult is going to carry a gaming handheld around with them in this day and age. The library it has doesn't even factor into it, though the Vita has not done itself any favors there. We live in the smartphone era, whether people on this board want to admit it or not.
Nintendo even took away Monster Hunter, which basically castrated the system in Japan.
3DS has a decent library. I find Square-Enix is the one dev that hasn't supplied quite as much support as they could have (where's Final Fantasy V/VI remakes?) but otherwise it's OK.
Kid Icarus Uprising, Monster Hunter 4, Mario 3D Land, Mario Kart 7, Fire Emblem Awakening, Luigi's Mansion 2, Resident Evil Revelations, Bravely Default, Super Smash Bros. 3DS, Super Street Fighter IV, Zelda: A Link Between Worlds ... I prefer the 3DS library to the DS honestly. DS did not have an original 3D Mario or Monster Hunter or Kid Icarus or Smash Brothers or an original Resident Evil or a Street Fighter.
A Link Between Worlds is considerably better than either of the DS Zeldas too and it has OoT and Majora's Mask remakes to boot.
The gripe I would have is that a lot of the Japanese games are not being translated over this gen (ahem, Dragon Quest VII).
Vita is a great piece of hardware, but really, Nintendo's next handheld will likely outperform it considerably, so that's not a big deal.
