SNES/Genesis graphics are some of the best in gaming history. They also withstand the test of time far better than most of the other generations.

I think gen 5/6, since 3D models got quite good and was often coupled with innovative and fun gameplay.

5th is greatest for me because of the pre-rendered backgrounds on games like Final Fantasy that I would argue age better than 3d worlds, and because of the art styles in Spyro and Crash Bandicoot that I do like very much. 6 also has a special place in my heart for having the first HD game I had ever played (Gran Turismo 4. It really blew me away). 7th is third place.

Graphics are there to just tell you what's on the screen and not to distract you with shiny details.

Same with the story. It should be there just so that you you know what's happening and why you're doing what you're doing. Any more story and the game isn't a real game.

So i'm gonna pick the gen when graphics and story were merely the colour of the paint, and not the painting. Gen 2.

Gen 4 for 2D and the latest one for 3D.

Honestly, probably seventh gen for me. It was a huge upgrade from sixth to seventh gen in my opinion.

Xbox era was the era where I was most impressed by graphics. Doubt you'd see another gen where a console had so much more power compared to others. SC Chaos Theory on PS2/GC looked like completely different games to Chaos Theory on the xbox.

I also like the use and emergence of HDR lighting and bump mapping and the shiny textures of that era. 

I liked the 6th gen because of the sudden improvement on 3D models.

Gen 4 for me.

SNES sprites looked very crisp and clear.

I'd probably go with Gen 4. I am such a huge sucker for sprites. I can play SNES all day and never get tired of them. A lot of my favorites are from that era too.

Gen 5 and 6 were excellent too as they were big leaps into the 3D with polygons and we got to see them polished more in 6. Gen 8 though, man, looking good...

Gen 6 brought us Cel Shading /thread. It also standardised 60fps as the target. A standard which sadly slipped again by the 7th gen.