I can't remember if on NA there was a thread on this, but I was watching something about Maniac Mansion and thought, geez I wonder how many other people would say Maniac Mansion was their favorite NES game. Then it got me thinking what other off-beat games might be peoples favorites. So if its SMB or Legend of Zelda, don't be shy to say it. No other better place to ask than this forum of Nintendo geeks, esp with a lot of us being very familiar with the library. You're #1 is not the "BEST", but what you love the most, for any reason, nostalgia, game play etc.
So yeah, Maniac Mansion for me. Others that are close would also be Zombie Nation, Mr. Gimmick, Dick Tracy and SMB 1 of course.
The weirder the better.