SNES.

Pixel art is still beaut.

The early 3D systems aged the worst with the N64 having a slight advantage in some areas.

The Dreamcast, PS2, Xbox, and Gamecube have aged decently, but the SD resolution holds them back. The Gamecube, Dreamcast and PS2 emulators have shown that the games can still hold up well if viewed in HD. Still waiting for an Xbox emulator.

The NES, Genesis and SNES have all held up very well thanks to their simple classic graphics. They are all still stuck in SD, but the SNES and Genesis have some absolutely stunning games thanks to some killer art directions. The SNES has a few extra graphical tricks up it's sleeve while the Genesis has stuff like the Sega CD and 32X that help it break beyond 16bit limitations.

I'd say the SNES and Genesis hold up the best.

For me it would have to be SNES, N64 and Gamecube, each have their pros and cons as to why.

SNES - pure classics that still play and feel great.
N64 - great replay value in a lot of games still.
Gamecube - some games on this system looked far better than many Wii games do today lol.

I'd say that the Gamecube, the SNES and the N64. In that order.

The Gamecube was a powerhouse back in the day, and it had games with a fantastic art direction like Wind Waker, Metroid Prime, Pikmin, Super Mario Sunshines and Super Smash Bros Melee. Some of those still see some action with my Gamecubes today.

Snes and Gamecube

Has to be the SNES. Dat 2D pixel art.

Absolutely this. I still play SNES and Genesis games via emulator nowadays. Beautiful graphics, art work and sound happened back then. Still like Terra's theme...

16-bit consoles have aged the best.

Original xbox.

Snes has aged the best but the Mega Drive aka Genesis would be second best.
I have just recently bought a Super Nintendo and am playing Turtles in Time Super Metroid, A link to the past and few other games. And they are still playable because of the retro charme. While games like Metal Gear Solid and Final Fantasy 7 are almost unplayable, if you where not a fan back then.