Based on games library for its time (no backwards compatability, no xbla/vc/eShop/psn ect) i have to go with the SEGA Megadrive.
Streets of Rage Trilogy.
Sonic Quadrilogy.
Outrun.
Golden Axe 1&2 (lets forget aboout 3 huh)
Shinobi III, Revenge of Shinobi & Shadow Dancer.
Eternal Champions.
Kid Chameleon.
Castle of Illusion.
Vectorman. ect ect
And those are just SEGA developed games.
Throw in 3rd party games like Micro Machines: Turbo Tournament, Street Fighter 2: Championship Edition & Road Rash and that pretty much sums up why it still reigns supreme in my eyes.
I don't expect the SEGA Megadrive to get many votes here, but it was very popular in the UK & Europe.