The most UNPOPULAR faction in Heroes 5.

Inferno. A spooky city...

And what do you expect from universal evil?:D
Mages are good because of magic. Mini-artifacts - I rarely use them. Now, the abilities that really rule belong to the warlock. Because
the knight has retraining - costs a lot of money
the demon has gate opening, a good thing during a castle siege, especially when you have Urgash's call
the rangers have avenger, I rarely use it because you need to kill creatures and run back to the town, and there are few creatures of one type; of course, if you kill several heroes and run back to the town, you can gain something
warlocks - can bypass magic protection + chains of elements
mages - mini-artifacts, depend on level + consume a lot of resources
necromancers - necromancy. a decent thing