I strongly, strongly favor IRC. It's well documented, well understood, I have servers already being used as game lobbies we can plug right into, it's easy to manage, I can manage it effectively etc. IRC scales. IRC is flexible.
While the RFC itself is obtuse, it is an otherwise well understood protocol, clients are easy to create (just look at all the VB and Java clients), servers themselves are well documented and understood, and it's darn convenient for the likes of me to get new machines tasked to the purpose

It's also in the best interest of the implementor to learn a widley used protocol

I will need convinced to use any other protocol.
That being said, lore is about to ship, there is a possibility I will be able to talk my programmer who implemented our IRC lobby code (all in script by the way) into coming over to the dark side of open source like development

-edit-
I don;t really feel strongly about much else technology wise. I do feel strongly about this
