There is only simple chat.
As far as I can tell, Simple chat is what everyone (who uses chat) has been using and it works well.
Java chat hasn't worked well since Java support became sketchy in modern browser.
mIRC was popular when PiemJi was around promoting it, but isn't being used much now as far as I can tell.
As GameTZ continues to slowly decline and I work toward transitioning us to a new server, I'm looking for ways to simplify the site. This is part of that effort.
Let me know if you have an issue with this.