JoeQuake is a regular Quake client, it can't do Quakeworld.
FuhQuake or EZQuake or FTEQuakeworld are good choices for Quakeworld, and a lot of JoeQuake is based on FuhQuake and the commands are almost identical.
Switching back and forth between JoeQuake and FuhQuake is easy because almost all the commands are the same in the two.
If you'd like to try a client that can do both Quake and QuakeWorld multiplayer, you might try FTE Quakeworld
http://fteqw.sourceforge.net/ which reportedly can connect to Quake 2 and Quake 3 too. heh.
Clients that can do that much stuff scare me