It's difficult to say unless you create an account on each server and look at the last page on the rankings to see how many active accounts there are. Feel free to do that yourself...
https://www.the-west.net/?page=register&mode=choose_world
This gives you an indication of the number of accounts ever created on a server, but not the actual number of active players. For example, it says that Colorado has 43069 players, but in reality it has 1725 active accounts according to the rankings. The newer servers will have more active accounts, but the quality of gameplay is lower. Still better than all the dead servers from Colorado and up, I guess.
I recommend Galveston if you want to start fresh though, since it's the newest one and people are still lower levels. only ~3-4k active players though