I think it would depend more on the kind of games you like to play. It doesn't matter one bit if Nintendo is "better" if your favorite game is on the Vita. So do some research, find some DS and Vita games you might want to play, and let those titles help you decide. BTW, the "3D" feature of the 3DS is cool, but you have to "train" yourself to relax your eyes to see 3D so go to a store and try this first before you plunk down your cash on it.
My son has a DSiXL but we don't find much games for DS that he likes, mostly just Pokemon. I would've rather bought a Vita, but it wasn't out when I got that DS