Can anyone answer?
Never was a big NES guy but the Mega Man series is my favorite series of all time and 3 is my personal favorite non-X game. I don't collect for the NES, but I'd be happy to take a Cheetahmen II off anyone's hands.
For SNES (greatest console ever made. EVER!) it's Yoshi's Island. ****, Yoshi's Island is in my top 5 of all time. Everything about that game is absolutely perfect... except the Poochy bonus stage, that **** can rot in hell. Right now Hagane: The Final Conflict is my #1 most sought after game for any system.
Although I had a 64 growing up I never liked it much because I always managed to buy the ****tiest games for it thinking they would be cool, but I do have very fond memories of 4-player Goldeneye and Majora's Mask. I am still on the lookout for another copy of Bangai-O that was stolen, and am dying to play Conker's Bad Fur Day, Paper Mario, and Banjo Tooi.
Anyone can answer for sure. Opening up more discussion I think can be good.
I probably should have answered myself as well.
NES: probably Metroid. I remember very fondly fighting through that to the end and how excited I was to make those end credits. Very tight second would be Castlevania.
SNES: I personally missed out on the SNES and N64 at the time. SNES days we went to Sega Genesis(also had Sega channel) and by the time N64 hit I was on PC. For SNES though I agree with Yoshi's Island.
Since I mentioned the Genesis I'm going to say Zombies Ate My Neighbors. So much fun and a LOT of levels to go through.
N64 I remember playing the hell out of Rush 2 Extreme Racing when I babysat my youngest brother and a couple of his friends. We had a lot of fun with that. Golden Eye was a big deal at anyone's house at the time though, that's for sure.