They were both great systems with awesome games on both. I had loads of fun playing both.
Most of my favorite games were on the SNES, since that was the console I owned. (Bonus, I converted it to play JP carts too. *^^*) However, I spent tons of time playing my bestfriend's Sega. ;P So, how could I just choose one? They both gave me equal amounts of fun!
I also liked Turbo Grafx/express.