Confusing: Originally, I would say the Water Temple from OoT. The first couple of times I played through OoT it was easily the hardest and most confusing temple I had ever encountered. Now that I have played OoT so many times, i find it's actually really easy, like most things practice makes perfect.
Easiest: I'd like to pick a different temple just to be different, but it's obviously Inside the Deku Tree. This temple is basically an easy tutorial.
Hardest: I would say Stone Tower Temple from MM and Turtle Rock from aLttP. These two temples gave me a lot of trouble. I had a lot of trouble with most of the aLttP temples, they just confused me and felt incredibly hard, but satisfying when I finally figured it out. Especially the stupid room where you had to light the torches while on that track, That part made me want to smash the game.
Easiest: I'd like to pick a different temple just to be different, but it's obviously Inside the Deku Tree. This temple is basically an easy tutorial.
Hardest: I would say Stone Tower Temple from MM and Turtle Rock from aLttP. These two temples gave me a lot of trouble. I had a lot of trouble with most of the aLttP temples, they just confused me and felt incredibly hard, but satisfying when I finally figured it out. Especially the stupid room where you had to light the torches while on that track, That part made me want to smash the game.