Everyone always says their faction is less mature / loses more pvp / is less active / blah. I wouldn't choose a faction based on who you think will have the better player base for what you want to do. As more and more people join, the demographics for your faction and server will begin to match those of other servers and other factions.
So chances are everyone else is playing on a server where all the other players share three brain cells. If its anything like WoW, the only difference between two given servers will be republic/empire ratio, depending on how "cool" the server name is for a given faction vs. overall faction balance. If Bioware named servers A, B, C, etc they'd probably get close to the same ratio on each server too.