I have little doubt that my favourite game of the bunch is going to remain Super Mario Bros. I've played most of the other games already, and I don't feel that they stack up, and that includes the original LoZ and Metroid.
Definitely SMB 1. I couldnt stand large games like LoZ1 and Metroid on the NES because they didnt have maps. It was just aimless running around until you happened upon something you needed to progress.