My favorite eneemy isthe horse but also the shadow dude!
wATS YOUURS???

well, first: Vergil on 20th mission
second I would say Beowulf... took a long time before I found out how to dodge his feather attack (just run around him so that you are positioned behind him very close. that's the only way he cannot hit you)
third nevams kiss attack... it's hard to avoid it the first times you play...

geryon(horse dude) was enoying at first, but once you learn to properly use ebony & ivory and trickster jumps you defeat him easy (no cheats, no jump -cancel)

the shadow guy is one of the easiest just keep hitting the things that make light appear and when you have lighted every one attack him. repeat it a few times and he is down.

Agni and Rudra are pretty fun unless you don't think to have 'em both way down before killing one off, then it's a royal pain. I like having the second one dead before he gets a chance to grab the other's sword.

But I enjoyed all the bosses, that's why my favorite level to play is 18 where you go and refight them all.