TMC, no contest. Great and original storyline, kickass weapons and items (how can being able to glide with cape or learn cool sword techniques like the Great Spin Attack be uncool?
), awesome dungeons and bosses, and great characters too. They all seemed to have a life of their own instead of just randomly being there like in ALttP. Also, Vaati was the coolest villain in Zelda history. Nothing can match up to his coolness. TMC is awesome in pretty much every way. Well, I guess the game could've been a little harder, but it was still the best handheld.
TMC is very underrated.