I voted SMB3. I'd call that the best game of the 8 bit era to be honest.
Honorable mentions for Mega Man 2 and Zelda though. The Zelda series doesn't need this, it's already got the best game of the 16 bit era and the best game of all time in it's locker!
Stuff that's not in the poll but worth a mention, even if it's just stuff I liked...
Pirates!
Robocop
Double Dragon
Battletoads and Double Dragon
North and South
The Adventures of Bayou Billy
Micro Machines
Rampage
Bomberman
Blades of Steel
Teenage Mutant Ninja Turtles
Gradius
A boy and his blob
Kid Icarus
Shadowgate
Duck Hunt
Castlevania
Maniac Mansion
Punch Out