It's hard to say which was the easiest one because all of the 3D Zeldas were quite easy, with Majora's Mask being the hardest one out of them (but still far from being as hard as AoL). OoT didn't have hard puzzles, and the bosses were all very easy, the only somewhat challenging battle was human Ganondorf on a 3 heart run. One of the reasons I haven't finished WW yet is the total lack of battles (the other being extreme tediousness - I noticed that you actually need those stupid treasure maps to beat the game (right?) when it was already too late and I don't feel like going through all the dungeons again to find them, just getting there takes eons). Twilight Princess had some nice puzzles, especially if you're going for 100%, try to find all the hard pieces and go through the Cave of Ordeals, but if you just finish the game without sidequests then it's a complete cakewalk. So out of the ones I beat, I'd say OoT.