I'm probably one of the few gamers who was a kid in the 90s that wasn't part of the Console War between the two. I owned a Super Nintendo and played the heck out of my Super Mario All-Stars/Super Mario World 2-in-1 Cart, which I say this Super Mario World was better than the normal one because Luigi had his own special sprite set. Anyway, returning to the point, I actually didn't know what the Genesis was until a new friend of mine introduced me to Sonic the Hedgehog 3.
I became a fan of both systems, but since I like more Nintendo titles than Sega titles, I'll have to vote Nintendo.