I don't consider the Gamecube, Wii U, or Vita to be flops. These were not systems that were dumped en masse by retailers, pulled off the market by their manufacturers, or put their companies out of the console business, or our of business entirely. Sure, they finished last in their generation, maybe even got lapped by their competition, but they finished their races. They sold millions of units, and many more millions of games.
Some of the real flops:
The 32X: put on fire sale in less than a year
The Atari 5200: discontinued by Atari in less than 2 years, in favor of the 7800
The Dreamcast: put Sega out of the console business
The 3DO: company formed, company failed (eventually)
The Jaguar: (arguably) put Atari out of business entirely
And I am leaving out the true flops, the many systems that died unnoticed, so poorly received that they're not even worth talking about.
Anyway, my answer is the Jaguar. When the Jag came out, I was thirsty as fuck for the next gen. I spent a lot of time with the Jaguar, and got a lot of enjoyment from it, even as I continued to thirst for the real next-gen systems. That entire period of the industry coming to grips with 3D rendering was a fascinating time to live through.