I dislike Ventrillo because, at least as of the last time I checked, there still wasn't a Linux/BSD client for it.
Teamspeak, though it looks less friendly, at least has a Linux client.
What we really need for this kind of stuff to work is an upgrade to IPv6, -every- computer having a 'real' (routeable) address, and an open framework, probably using speex or something like it for the actual codec.