Wii to WiiU was certainly a pretty big jump. Definitely amplified by the fact that GC to Wii jump was tiny.

Many many years ago a buddy called me over to see his launch xbox 360 playing pgr3 and fight night on a HDTV it was absolutely mind blowing the clarity difference from what I had at home

Definitely the jump from the SNES to N64.
Whilst Sega went from Genesis to Saturn, the N64 was a far larger leap forwards.

The Nintendo 64 wasn't really Ram limited.
With the expansion pack you could have 8MB... And the system can theoretically support around 12-16MB which is the upper limit from the initialization routines on the system itself... The Nintendo 64 was able to be fairly memory efficient as it can stream data directly from the ROM carts with no load times.

The issue was that stupid 4kb of texture cache... With a unified memory architecture it was a stupid and unnecessary decision.

In saying that... People have been going back to the Nintendo 64 and "optimizing" nintendo 64 games by making them more efficient as the Nintendo 64 had a comparatively modern memory hierarchy that developers didn't really come to grips with until half way through the PS2 era.
I.E. Taking Mario 64 and making it run at 60fps on the real hardware.
https://www.youtube.com/watch?v=t_rzYnXEQlE&t=724s

Gotta' remember that the SNES had single cycle memory, so the N64 was seen as slow and high latency by comparison.

With Switch being a small jump from Wii U (it's pretty much a Wii U Pro), fingers crossed we're in for a big jump with Switch 2.

I'm going to be really bummed if Switch 2 in docked mode only hovers around Xbox One/Xbox One S territory. And if it's even a little below that (but well above a Switch) that will also be disappointing. I feel like PS4 is the floor for what Switch 2 in docked should be, with PS4 Pro or above as a realistic ceiling. 

People are kind of ignoring handhelds, but it may be the GBC to GBA. Look at something like Donkey Kong Country on GBC to Golden Sun. That's a pretty huge gap.

For me it was the SNES to N64. That 3D jump was 1 of a kind.

Followed would have to be the N64 to Gamecube. Seeing games like Luigis Mansion looked like a Pixar Movie.

@bold: Oh, that's really interesting. If the leap is judged by quality, then that's a totally legitimate pick. The NES generation was hugely important for the industry, but it can't compare to the SNES years, which delivered masterpiece after masterpiece.

Judged on a technological level, I will be boring and echo the majority of posts: SNES to N64. I can't really put into words how the leap from 2D pixels to 3D polygons shifted how I understood and appreciated video game design and art. It blew the back of my head right off when I was 13.

The last time I felt anything similar was the jump to HD in 2005/2006. Since then, it has felt very much like diminishing returns.

SNES to N64 and PS2 to PS3, hd gaming also did a lot and the difference between God of War 2 and The Last of Us is still very big.

3DS to Switch is also a huge gap, since the Switch is also a handheld console