The boss whom I enjoy battling the most is Ghot, I find fighting him is refreshing for a boss battle in a Zelda game. It's intuitive relative to the Zelda games that I have played and completed in the past, and I find it to be a very fun battle. It is probably aided by the fact that I also prefer to wear the Goron Mask over the other two race masks. I can't really explain what I find more fun about it.
I'd have to say Ghot. Ghot was a big challenge for me... I might suck at playing Zelda (any game at ALL!), but this boss took me exactly a week and 2 days to figure out how to beat. Majora, on the other hand, was too easy for me.
My favourite boss was gyorg because of the challenge. I also thought that he had the best way of beating him odwalla was just too easy as hylian link and I could never find a use for the deku form in that fight. In the ghott fight in human form you could just stand at the entrance and use fire arrows without tge posibility of getting hit and the goron form I felt that the fight was too easy for the forty percent of the main story checkpoint. In the gyorg fight the fight and temple leading up to it were so well designed and a fine ballance of challenge and fun,the fight as a zora or using the zora form was a great idea, a healthy challenge in an otherwise straightforward game, and lots of fun. The twinmold fight just wasn't a good idea and a terrible way to end a fantastic temple. I didn't like how you needed magic to fight him (I don't usually get the magic metter upgrade) and I kept running out of magic and disliked the area to fight him.