Vaishan. I can't imagine how he'll perform in the endgame, but he's decent as a scout in the early game.
Posts from Which hero is the best in the Tribes of the East expansion?
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I think it's better for a Warlock not to play in the late game at all. But if you have to choose, then Sorgalla: you can theoretically upgrade his Retribution skill, and he doesn't have Chaos magic initially, which will allow you to learn Summoning without any obstacles. And lizards are still...
They have a special unit tailored for Chaos, but it's difficult to effectively use Chaos in the late game. Nevertheless, it can be challenging to play without Chaos sometimes (at least for me ;)). And overall, it's not the easiest faction.
A standard set that is usually offered: Necropolis, Stronghold, Fortress, and maybe Humans as well.
I mainly play with Synitar, but recently I've also started enjoying Leto (a combination of plague and invisibility).