Overall, I'd say Gen 7; we started out with essentially just HD versions of PS2 games, and ended with things that really pushed the boundary of graphics, story, and gameplay. And there was that whole motion control thing that I think in retrospect most of us would rather forget had ever happened, but was still emblematic of a generation where it really felt like the industry was trying new things before going in a much safer direction from Gen 8 onwards.

That said, Gen 3 is a very close runner-up. Compare the graphics in the first Super Mario Bros to something like Castlevania III, and it's staggering to think they come from the same console.

Gen 7, but only for PS3/Xbox360. Not including the Wii.

I don't know if there'll ever be another significant gen like that ever again.

I actually really liked the motion controls on Wii when they were well executed, which was something that did improve a lot over the course of the gen both with devs figuring out more optimal uses and the introduction of motion plus in 2009.

Wii Sports Resort was a big leap over Wii Sports 1 for instance, while FPS controls improved hugely from early efforts like COD3 and Red Steel 1 to later efforts.

I still like them, they paved the way for VR to emerge on consoles. PS3 move controllers with PSVR1 worked great. 

There was also the Balance board, great piece of tech, simple durable and perfect for snow boarding games.

I am also gonna go with the seventh gen (although I acknowledge there is a good case to be made for both the third and fourth).
We went from Call of Duty 2, which looked good for sure, but we ended up with stuff like Assassin’s Creed Black Flag, GTA V, The Last of Us, Rise of the Tomb Raider, games that don’t look all that different from what we are still playing.
But also on aspects besides the graphics. In the start games ran off discs, by 2013 they could run off the hard drive for improved performance. At launch we could buy tiny games on the online store fronts, by the end you could buy any game that way.
For better or worse we saw the rise of DLC and games as a service.
We certainly also saw a huge jump in alternative ways to control games, the Wiimote was revolutionary from the start, but Motion+, PS Move and Kinect were certainly significant jumps.