Mynos
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Hmm... I wouldn't choose to play as Haven on S or M maps. Genies are cool, but they're quite expensive, and in small numbers, they're even worse than Imps. Besides, they're not that effective against Necropolis.
But overall, it all depends on the game version and the map. If you play on a "beefy" large map in Heroes of Might and Magic, Necropolis can gather a lot of Vampires, as the hero can summon them from level 8 (this was fixed in the expansion - from level 18). Chaos, on the other hand, is obviously weak on large maps - Chaos Demons don't get stronger with magic, and magic is generally useless against enemy heroes.
But overall, it all depends on the game version and the map. If you play on a "beefy" large map in Heroes of Might and Magic, Necropolis can gather a lot of Vampires, as the hero can summon them from level 8 (this was fixed in the expansion - from level 18). Chaos, on the other hand, is obviously weak on large maps - Chaos Demons don't get stronger with magic, and magic is generally useless against enemy heroes.