If we go by what was more profitable my guess would be Wii U. If we go by "success" I'd have to say Vita wins that cripple fight. The drop from PSP to Vita (80m > 12m) while terrible is less terrible than the Wii to Wii U drop (100m > 10M). Also the Vita utterly destroys the Wii U when it come to number of releases so from a gamers perspective I have much more to play.
PlayStation Vita Japanese Software Sales (Media Create Physical/ Famitsu Digital)