I've found using hipchat with coworkers to be much nicer than using XMPP with coworkers mostly for it being closer to IRC: there are rooms where most discussion takes place, so you can get to know people by lurking there, and when you need to 1:1 message someone, you probably have some context about who they are, which makes a world of difference to an introverted new hire. The realtime team-wide chat just makes everything feel much more friendly, imho.

I'm sure it's possible to get that setup with XMPP, and it's definitely possible to get an equivalent setup with IRC (which I have an external server running ZNC for), but it's not out of the box, and there is something to be said for having a good configuration set up and working for everyone out of the box.