I haven't beaten OOT, just played it at a relative's house, but from what I've already done, I'll say Barinade, as it is a gross, genderless, weird-looking parasine inside a giant fish, and it wasn't too hard or too easy to fight, and its vomit-inducing death sequence worked just fine with its theme, and the fact you kill it mostly with an austrailian toy found inside Jabu-jabu. other than that, I think a similar Favorite boss in OOT poll has already been made.