The Dreamcast by a huge margin.
The hardware was a massive leap beyond the consoles that came before it.
We went from low-res glitchy polygons and no texture filtering on the PSX, and super low-res, muddy, low-poly, and low framerate 3D on the N64, to high poly, high detail games running at a high resolution - often at 60 FPS. In PAL regions, it was the first time for 60 FPS on a console at all. (outside of mods) It even did progressive video with the VGA box.
It was a leap in performance like nothing before or since.
And on top of that, the console was tiny! It was a real technical marvel.
It was released at a time in my life where I'd be playing local multiplayer with friends every weekend.
When I didn't care about setting money aside for the future, and all of my income after covering that month's bills was seen as disposable.
The import scene was huge back then too, with all these obscure and interesting games coming over from Japan.
I had something in the region of 100-150 games for the system, four controllers, a pair of light guns, a pair of arcade sticks, and a keyboard & mouse.
It was the best local multiplayer system of all time, and the single player experiences were great too.
There was a massive variety of games in its library, and it was the best time for arcade-style games that there ever was.
Phantasy Star Online was just magical, and nothing will be able to recreate that experience again. Online gaming like that for the first time on a console was just amazing.
I can see why people might look back on it now and say that they don't want to play many of the games now - or that there might be a better version on other platforms today - but that ignores how big a deal the Dreamcast was at the time.
The Wii U is almost the opposite of the Dreamcast for me.
It was a technically inferior system when it launched and many of the games rely on gimmicks.
It's no fault of the system, but nowadays, local multiplayer rarely happens. People are too busy with their families to meet up for local multiplayer - even online multiplayer is difficult to set up with more than one person at a time now.
The controllers severely limit the types of game that you can play on it in multiplayer anyway, and the multiplayer is often asymmetrical with one player on the gamepad and the others with Wii Remotes.
If anything, the Wii U is at the top of the list of most disappointing consoles for me. There are probably fewer than ten games that I care about for that system, and many of them were disappointments due to stupid design decisions from Nintendo - like how poorly the online component of Mario Maker is handled.
It's full of safe and lazy sequels from Nintendo. Sure, they might be good games, but that's also really boring. There's very little from third parties at all.
Extra context: Dreamcast for its era was ahead of even PC gaming for a period.
Yeah... I don't know about that.
I had a GeForce back then which was a lot more powerful than the Dreamcast,
running games like Quake 3 at smooth framerates and much higher resolutions.
The Dreamcast versions of Quake 3 and Unreal Tournament were pretty rough.
As a console experience, it was a massive technical leap though.