A lot of people are going to say Wind Waker but I thought it was actually pretty challenging (especially the triforce treasure hunt.) Twilight Princess might have been the hardest for newcomers but people who have played OOT, MM, and WW have already seen all the puzzles Twilight Princess threw at you. Really I thought TP was way to easy because it was just more of the same stuff we've done before in previous Zelda titles! One really sad thing is you can kill enimies in 2 simple sword swipes, which was a first. There also really wasnt a lot of puzzles, and when there was, Minda just explaind how to beat them (same with bosses!)
Twilight Princess: The easiest Zelda yet!