Dom-I - Atlantis, I remember playing the demo for many months befor I've ordered and how much, oh how much I wanted to recruit their best mages and units.
Dom-II - Pythium, I like their Byzantine flavor and their astral royalty.
Dom-III - Pythium, I think it wasn't changed at all but I like it no less. I'm a bit disappointed that they don't have an early and late ages. I am forced to change my strats of playing them due to the old age mechanism, but its actually not that bad.
Dom-III, Abysia EA. My first time playing abysia since Dom-I. I saw the demonbred assassin and the weird lava-warrior replacment and panic ensued, "What have they done to my abysia?! Noooo!" then I started a middle age game and all the oldies were back .
I can understand why Pythium doesn't have an early age, as they are a splinter from Ermor, but I don't see why they couldn't have a late age version. Maybe with a middle eastern/Turkish flair, since historically the Byzantine Empire was conquered by the Turks. The units wouldn't really be legion troops, but it would be a cool extension of the historical theme, and would introduce a culture to the game that I don't think it in it at present. The whole serpent angle can be kept in for consistency.