Definitely Virtual Boy but I knew what I was getting into when I picked one up, I just wanted to complete my Nintendo collection. It's actually not that bad, but it's easy to see why it failed.
I guess my tastes run contrary to a lot of people here, because Wii and N64 are probably my favourites. I like seeing something new in gaming. N64 did have really awful third party support, though. I have a bit of a Jeckyll and Hyde relationship with it.