Unofficially. There are no pve, pvp, rp servers for FF. Besaid was just dubbed the RP server at launch to kinda get most of the same people onto the same server. As far as popularity, Rab is actually a pretty popular server. You've probably got yourself tucked away in some nook in Gridania, don't you? lol. Head to Ul'Dah no matter what server you are on, that's where everyone is.