Currently FuN have an ET server, a CSS server and a CoD server.
You can see who's playing on them currently on here -
http://aaed.co.uk/
You'll also see below that the Mobsters servers, who are old pals of FuN and you'll see there are three different uo servers with a good number of players and catering for a variety of different game types and maps.
If you only like uo, then check out the mobsters servers, but if you like any of the other games, then get yerself onto the FuN servers