In your opinion, which faction is the strongest in Heroes 5? Let's discuss the advantages and disadvantages of each faction.

I believe that all castles in Heroes 3 and Heroes 5 are strong in their own way. It's important who commands these castles.

Enough of beating around the bush on this ambiguous question!
The question needs to be asked more specifically, and then the answers will be clear.

For example: Which castle is the strongest against...?
or Which race is best for defending in a castle?