I'm on Facebook, Myspace and Flickr.
I was a Facebook fan first as that's where I started and it took me a while to get my head around Myspace. Facebook is more user friendly but you can't customise it as much. I find I get loads more 'reward' networking on Myspace too. I think Myspace is my current favourite.
Facebook is still good for the groups though - finding out what's happening at burlesque events around the country or what other performers/fans are up to.
I haven't really paid enough attention to my Flickr yet, I need to sort it a bit better and don't really use it for networking...I get people talking to me there but not the sort of people I enjoy talking to
I also blog using Typepad but at the mo this is set to private for my close friends only to read, but I'm working on a public one to be revealed probably in September.