Genesis vs SNES was the most heated of all time I think. Sega used every chance it got to smear Nintendo. Nintendo didn't do too much smearing, but their marketing was just as fierce. Since in this generation, the technology was able to bring the arcade home. There where already 2 sets of fanboys.
Here were their arguments that I remember:
Genesis:
-Played sports games better
-"Blast Processing"
-Mature titles availble, Mortal Kombat had blood while the SNES version removed it, along with lame "Fatalities"
-Sonic, mascot with an edge
SNES:
-Played RPGs better
-Mode 7
-Mario
-Played Street Fighter 2 better, this made a huge difference
Wii Code 8761-5941-4718-0078