It depends of what you consider as "being better"
Vita has better technical specifications, processing power, control options. Then it´s technically better.
3DS has a better library of games, plus it is backwards compatible and it´s cheaper. From a product standpoint, 3DS is better.
I disagree the statement that 3ds "doesn´t have AAA titles". Since when AAA titles refer only to shooters with realistic graphics? AAA titles are games that exceed in design and production excellence. Fire Emblem Awakening, Super Mario 3D World, Kid Icarus Uprising, Shin Megami Tensei IV, Resident Evil Revelations, Etrian Odissey IV, Animal Crossing New Leaf, Monster Hunter 3 can all be considered AAA titles.