It goes Asura -> Bahamut (70% of Asura) -> Everything else (roughly 50% of Asura)
Database
These are estimates, but jive pretty well with reality. Asura is filled with Mercs (sell you clears for gil) and yell spam, Bahamut is a tamed-down version of Asura, and everywhere else is pretty much socialize-or-die.
If you're just looking to do story stuff or solo/low-man, you can go anywhere and I'd recommend a more chill server.
If you're looking to do end-game content but have the desire to lead, do research, and/or find friends/linkshell/static, I'd say any server will do.
If you want to join PUGs for end-game content, Bahamut or Asura are probably your only options, though keep in mind gear requirements can be very strict so it will probably be a *** to get to that level. You will need to find a very supportive group or be prepared to spend a *** of gil, and probably be restricted on which jobs you can get a group on until you're extremely geared.