Wyverns

So, I created two heroes in the editor: I gave one 60 Phoenixes and the other 60 Dark Wyverns, and ran several duels. In all cases, the Dark Wyverns won convincingly, and if they attacked first, there were an average of 20 of them left at the end. If the Phoenixes attacked first, there were still 20 Dark Wyverns left (once, 17). The poison and, to some extent, regeneration did their job. The heroes had the same stats, and they didn't participate in the battle. From this, it follows that in a one-on-one battle, Dark Wyverns are more effective, but it wasn't possible to use the two unique abilities of the Phoenixes – corpse consumption and electric breath, so the conclusion is: the upgrades are, in my opinion, equivalent; I think the game stage plays a big role here. If not much time has passed, it makes sense to take Dark Wyverns – as mentioned above, it takes 600 health points from a dead unit to resurrect one Phoenix. Electric breath is divided among the units, so the damage from it isn't that great. Or, if you have to play against an aggressive race (like the Elves), you can also take Dark Wyverns because you'll most likely have to play defensively, and there won't be time to use the Phoenixes' corpse consumption ability.