i actually really loved all of them. If i had to pick a favorite, it'd be Tenalus, even tho he look's like he's from Monster's Inc.
my list from favorite to least favorite is;
1.) Tenalus- Loved this fight, loved originality, and how ship ripped in half. Started in boss room, ran back to ship's deck. Awesome
2.) Ghirahim(any phase) Awesome sword fighting boss, loved all 3 battles with him.
3.) Koloktos- Epic, and weird, was not boss I was expecting at all, I loved that.
4.) Demise- Epic finale, awesome 2nd phase, really tough, very climatic, I loved it, only thing was he was a bit too much like ganondorf
(Anyone of these top four could've been tied for 1st, but the rest of the bosses didn't make me have the same reaction. These 3 are the bosses i like less than the first 4.)
5.) Levias- I thought this was pretty cool, only boss fight while flying, although i expected more like that. loved the music, but a pretty straight forward fight and not quite a 'great' battle.
6.) Scaldera- I liked this boss more than I thought I would, I actually had trouble with him when the battle started, but once you got what to do, it was too easy and simple. I like boss fights that change phases and challenge you in a new way each phase, which this fight didn't have. Plus, I was disappointed the boss wasn't a dragon, because I thought all signs pointed to that.
7.) The Imprisoned- I didn't dislike this boss, but I didn't like it either. 3 phases, i loved how it was an overworld boss, but the monster itself didn't intimidate me. Cool original battle, and loved the spiral, but I thought these 3 fights were really easy.
(These bottom two were the only two bosses i disliked)
8.) Moldarach- This boss surprised me since i was expecting a technology type boss, and i didn't really like the fight that much, hitting the claws was kinda fun, but lost it's touch and got repetitive. And a boss digging around in the sand isn't exactly original in Zelda either. Disliked it, but I don't hate it.
9.) Bilocyte- Unoriginal except for the fact you were fighting on a whale's back. Really easy, and overall a pretty lame fight. I can honestly say this is the only boss in the LoZ series that i can say i hate. (not because of difficulty, just boringness )