Link to the Past. Definitely, no question, it's a fact of life. Link to the Past is probably one of the greatest games ever made.
I feel I should say something about Ocarina of Time...I don't find it overrated, excepting in the fact that people claim THAT as the best Zelda game. It's 2nd best. It's a fantastic game in it's own right, I don't quite understand why people don't like it (calling it the FFVII of action games is over doing it). Great game, definitely.
And lastly, only one person (that I saw) mentioned Majora's Mask so far, and that game is truly under appreciated. It didn't feel as good as Ocarina, to me, but it came damn close.