Interesting debate! But wouldn't it be better to base our arguments on facts? The fact is that the question of which faction is better to play arises only in the early stages of the game, as by the end, it doesn't matter – the hero uses both powerful magic and combat skills equally.
However, here – in the very beginning, and at the moment when a full-fledged army is just being formed – in my opinion, the question of which faction to play – mage, warrior, battle mage – is crucial.
Personally, I prefer mages. Advantages: magic, which compensates for the weakness of archers (if any) or replaces them. Option: battle mages with the same advantages. You can attack even creatures that are more powerful than those in your army.

Best regards, Draco