Ikana. By far. My second favorite is Woodfall.
Ikana was just so mysterious and brilliant. It had a deep, hidden story that only got partially revealed, and I'd love to see more of it. It had dark elements, and cool undead themes. Great music, and one of the best dungeons of the entire Zelda series, IMO.
I would really like to see more from this area sometime in the future. Perhaps another Termina game? Maybe even one that focuses on this region... now that would be
excellent.
And I also really liked Woodfall. I've always liked the Deku, and they're presence here just made the place cooler. I also like swamps, and using a swamp instant of a flat out forest was a nice change of pace. Oh, I also loved the Deku Palace (especially the song!) and Odolwa, the boss of Woodfall Temple. One of the neatest bosses in the series, I've always thought.