I use MGT because I own the network. It also is populated with independent game developers, mostly TGE licensees, but some others.
It's a moderated server, there are few morons, hackers, etc, which makes for a pleasant chat. Spammers, virus distributors and warez monkeys are not welcome.
That's where I go for development questions. It serves a very specific purpose with a very specific clientele

As far as QuakeNet, go for it, I'll need connection details, if people are actually using it, I'll login there.
But you can, indeed connect to multiple IRC servers with any IRC client
