The Vita 100%
From a gamer's perspective the Vita did better in Japan than the Wii U but the Wii U is doing better in NA than the Vita and this situation imo favours the vita a lot.
The vita is still supported by Japanese developers, I would say the Vita is in a much better position when it comes to games even though the Wii U is doing better in NA that did not make Western publishers consider the Wii U as a viable option and chose the PS4/XB1 instead.
The Wii U might end up outselling the vita (or maybe not ) but in the end the Vita will outlive the Wii U thanks to Japan and all the games they are bringing over.
Edit: successful in terms of games