I have only seen one 3DS owner and one Vita owner ever. Both of those persons were me. I also play my handhelds nearly exclusively at home. Tried both on the train but I can't get a steady 3D effect with the 3DS and I can't see shit on the Vita when there is even a little sun light...so I guess they both fail for me as true portables.
Ongoing bet with think-man: He wins if MH4 releases in any shape or form on PSV in 2013, I win if it doesn't.