I have too many favorite units, much more than 5 - so it takes much more than one playthrough to use them all.
My absolute favorite unit (at least as a mage) must be the Necromancer, because it allows you to play with some attitude! Destroy an enemy stack, raise it and put Kamikaze on it! It gives me the same feeling I had when I was playing Jagged Allience 2. That game was full of attitude and sarcastic comments - where the most memorable is Ivans dry "Buy Buy" when he had just killed an enemy
My current setup as a warrior is rather standard, with
Demonologists
Paladins
Inquisitors
Royal Griffins
Cyclops
Earlier I had 4 Archmages instead of the Demonologists, but since I could not find more of them and because the Guardian Angel medal is completed I exchanged them. Currently I do not need the shield. Will probably put them back in for the boss fights...
I have also played with the following teams that were great:
Vampires
Ancient Vampires
Black Knights
Bone Dragons
and the Necromancers!!!
Choshas
Tirexes
Brontors
Hayterants
Inquisitors
Elfs
Paladins
Inquisitors
Green Dragons
Red Dragons
I do not like the high level units of the elves (Ents and Ancient Ents). They are too slow and burn too easily. Have anybody any good experiences with them?