For me, it depends on how complete the factional unit rosters are. I read a while back that not all factions will have all units available on the first release.
I will pick a faction that is 100% complete, which has neighbouring allies/enemies who are also 100% complete. I don't mind which faction that turns out to be.
This is not a criticism of the EBII team - I will be playing EBII for the next 10 years, and as a completionist, will eventually play all the factions.
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