Which level 5 monster is the best?

It's hard to choose. Minotaurs are great because they have good morale and attack. Gorgons with their breath attack are just devastating. Thunderbirds are also good – they're fast, and lightning helps. The Djinn with its spells is an excellent helper. The Lich with its cloud attack is just brutal. Demons summoned by the Hellspawn sometimes save the day.
I'll choose Fanatics because they represent my favorite castle and are also good archers and fight without any penalties.
I like Dendroids the least because of their speed.
By the way, where are the Trolls? They're also level 5 and very strong, and it's a pain to kill them.