Which creatures from the alternative upgrade options do you choose?

Hmm... I definitely remember that five of them died. So, a normal attack would have killed 20 dragons... :-) Maybe I'm confusing the number of Hydras... Well, and my attack was definitely over 30. And the dragons attacked the Hydras only because I had deployed them alone. The benefit of poison is that the enemy doesn't want to attack them, but if they do, it's free damage. Imagine how many lower-level creatures would die? And regeneration is only a meager 30-50 hit points each (and quite rare) turn for the Hydras. This can only be useful with very small armies where every unit counts. So, at least for me, the choice is obvious. As for the Dark Mage... he will still have to destroy the Hydras at some point. Well, he cast Blindness on them, so he won't touch them for now. We'll chop him up with Chaos magic in the meantime. And by then, there will be nothing left to kill the Hydras, and their ability will make itself felt (especially for the Necromancers with their low hit points).

Added after 34 minutes
And they really messed things up with the Riders... They deal a quarter of the damage to all enemies in their path instead of ignoring defense! If the alternative Riders dealt full damage, I wouldn't have taken them. So, the choice is obvious here too.