Best way to rotate about a node?

Hi, I want to attach models to childnodes in my game world, and set a rotation value for each, what is the best way of doing this?

When I say best way, I mean the most concise method, because I'm building a Darkstar server to transmit the rotation value from the server over the packet protocol, and I need the value to be as small in size as possible, but contain all the info I need.

I've seen a few methods, but just want to get the genral consensus…