I like how this doubles up as a forum server census.
Top three so far seems to be Ultros (duh), Excalibur, and Balmung. Happy to see you fellow Balmung-ers!
FFXI: Exodus @ San d'Oria since November 19, 2003, Siren Server
FFXIV: Turk Kalahai @ Gridania, Balmung Server (RPC Link
Rift: Kalahai @ Sanctum, Faeblight Server