I will admit Vita is more powerful than the 3DS, but pretty graphics mean nothing when it comes to a great game, and so far, I think Vita doesn't have it. Not to mention how expensive it is compared to the 3DS's current price. Personally, I believe that quality gaming trumps power and graphics any day. For what it's worth though, the 3DS has awesome graphics for its firm ware, play Resident Evil Revelations and you will know what I mean.
One of my friends bought a Vita and I held it in my hands. It was a little cumbersome, but hey, whatever floats people's boats if they want to play Call of Duty on the go. :/
There are many great titles on the horizon for the 3DS, and what I see coming to the Vita is a few dry and cut titles that are pretty much clones of what is offered on the PS3.