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The Wii U and the PS Vita. In the end, I have mixed feelings for both and both didn't live up to their expectations. But I don't regret buying them.
The Wii U was a huge letdown for me. The system was slow, the gamepad hardly ever used outside of a few games and a lot of Nintendo games were underwhelming for me. Most of the good games got improved Switch versions later. You could really feel Nintendo was a) struggling with HD development and b) focused its resources on the 3DS at the time. I did enjoy some games, though: Wind Waker HD, Mario Kart 8, Mario Maker. Nintendoland was also a decent game. Overall, my least favorite Nintendo system of all time.
The Vita was also a disappointment after the really great system the PSP was. The only games I liked on it were Gravity Rush and Persona 4... and I finished neither of those games lol (finished P4 later on Switch). What I did enjoy most about the Vita was the PSP library and the fact that you could play PSP games on the bigger screen. Do I regret my purchase? No. But I wouldn't say it was really worth it, either.
