Oooo google hangouts is a good one!
I like the idea of teamspeak, if it just means that we can dive into a party/lobby/group (don't know what they call em)
I was on skype last night with josh and matt and it all worked perfectly fine, i've saved them as a group so i can ring groups instead of individual people. If they're not on then it doesnt ring but will call everyone else.
I've only used google when speaking to my missus and that worked fine but it was only with one person, so i don't really have any pros or cons.