Turtle Rock was hard for me, but I'm surprised how easy it was compared to Eagle's Tower. Eagle's Tower was the nightmare for me, it gave me a headache and I had to resort to a guide twice - once again a kick in the nuts for me as soon as I found out how easy the things I missed was.
All the...
Okay, I'm changing my choice to Link's Awakening as the hardest. I haven't died so many times before ='(
Still, it's a Zelda game, and it's interesting enough to keep me playing or from giving up.
I've just started LA, I've just done the second dungeon. So far, it's quite challenging, and strange. Enjoyable though.
Of the ones I've played in that list: PH, MC
MC was hardest XD.