Okay, looks like I'm gonna have to make the push for OOT.
A Link to the Past was really the first Zelda game that was really widely accepted. It was pretty accessible and tons of fun. It had a lot of dungeons and set forth a great majority of the staples of the series.
Link's Awakening is probably the one I've played the most just because it's so much better than all other gameboy games.
The Ocarina of Time was a game that had been delayed for years and it was a game that had an impossible standard to live up to. It was one of the only games I've known that lived up to the expectation. It was just about as novel an experience as could be had in gaming. It tried so many new things and it did them all flawlessly. It took Zelda from fun to epic. I created a flowing story, a cast of characters and it was by far largest Zelda world ever. In a day when games were usually just games it was an experience and it was one that was completely unparalleled.
Think back with me, the deku tree, the goron cave, the desert fortress, Ganon's dark world, restoring the world to light. The game went on far longer than anyone expected it to and it dwarfed every sequel in scale until Twilight Princess some years later. Ocarina of Time was the most complete, epic, fun and novel Zelda game and possibly the best game ever.