Going to push the envelope pretty hard - the NES.
I have hundreds of real carts, many rare, and I don't find myself ever playing the thing. I'd rather just play Genesis or SNES. I blame composite. Once I got setup on SCART/component I can't stand composite video. I bought a Master System and a good number of games to replace the spot in my heart the NES held.
Shinobi III is in my top 5 Genesis titles. I'd could play it all day long and never tire of it.