Battling Ganon/Ganondorf has been pretty epic to any zelda game. But I also like battling other enemies like Majora's Mask, Twinova, Bongo-Bongo, Queen Gohma, Twinmold, and others. But Ganon/Ganondorf is my fav boss battle
Definitely all of the forms of Gannon in Twilight Princess. It was very fun playing through what seemed like endless battles against him (all of which were very creative).