When PSP was annonced the majority expected that DS will lose so this time the majority expect that 3DS will win so PSVita will win.
Sony is not a week company if their console has more better games then Nintendo and have a good price i don't know why Vita will lose.
Sure fans of Pokemon or mario or zelda will buy 3ds for thats game but gamer who's not pro-something won't buy a console for one game.
PS4 - over 100 millions let's say 120m
Xbox One - 70m
Wii U - 25m
Vita - 15m if it will not get Final Fantasy Kingdoms Heart and Monster Hunter 20m otherwise
3DS - 80m







