Obviously the Wii U is stronger just from the fact it has more 1080p/60fps gaems then the "next gen" consoles.
Proof? just look below. This obviously means Wii U is the stronger console FACT, those supposedly next gen consoles cant even run in 1080p/60fps lul
Wind Waker HD: 1080p/60fps
bayonetta: 1080p/60fps
vs
Killzone SF: 1080p/30fps
Ryse: 900p/30fps
Wii U better confirmed.