Eh, my favorite was Pythium Serpent Cult, WHICH I SEE IS NOT HERE ANYMORE!
Perhaps a mod will show up and put them back in. There is a few units I sorely miss. I didn't like the default Pythium very much.
So far I like ME Ulm a fair amount (still, really). Early Ermor reminds me of the good old days so I play them occasionally.
My own nation which is fairly Ulm-like. It "works" but is in desperate need to "cleaning" up now that I have a bunch of new modding commands available
I'll finish and release it someday.
Lets see... Agartha Ktonian Dead has neat stuff within.