Vaulters for me i found pilgrims pretty boring imho and i liked their missions and their unit designs united empire is my second choice cant never get bored of evil humans well to be honest my first choice would be the horatio but they re more transhuman than anything. 

I agree, I really like Pilgrims and also lean Vaulter (especially Mezari in terms of  vs .  There seems to be a decent sized fan base for United Empire (on the forums overall) so I think it might be worth considering all 3 but I would prefer less explicit human races than more.  Additionally in a game which will likely only have 8 concurrent factions in one playthrough, I think the number of human races should be at a conservative amount.