The Wind Waker. Yes, I'm one of those people that seem to think that a cartoony, simple game is the best...xD
Really though, I just liked the characters, style, and story. Easiness beside, it still seems the best to me...
The other games are still good. I will admit that I've played OoT the most and have only completed TP 100%. MM, like WW, does hold a special place in my heart, but I don't like it as much. It's an awesome game, but it might just be because I came to beat it later that I don't like it as much. I still have my old golden edition for the N64 too (but never beat it until I got the collector's editions for GC). Moreover, I just feel like I haven't played SS enough to make a valid judgment on how I think it measured up to the other four. It might be better, but I found certain things in it downright frustrating (in a bad way) though it still seems to be a worthy Zelda game...