Neither, by preference. The DS and PSP both still have a lot more going for them at this point. Maybe someday someone at Big N or Sony will get a sudden rush of brains to the head and come up with a reason to buy a new generation portable. Or just wait for hackers to defeat the region lock on the 3DS, and enable backward compatibility on the Vita.
Backwards compatibility. One has it, the other doesn't.
for this ^ reason, 3DS, if you HAVE to pick one, even though it's region-locked.
. --- I'm waiting for Bandai to release the WonderSwan/SwanCrystal II and blow both the Vita and the 3DS away.