SOrry to be a broken record, but Sococo's product does all of this. IT uses P2P when it works; else it routes through a 'media node' when necessary, all automatically and on the fly. You can be walking around with your wireless laptop on VPN talking and video-chatting; stop at your desk and plug in, and all the streams switch almost-seamlessly.

Caveat: I work at Sococo (I architected the audio/networking system).

I've used Skype and Google hangouts before and haven't had issues (although I've been just screen sharing, not screen + video). If you have audio problems, you should get a headset. Even cheap ones are better than most laptop microphone / speaker setups.

Have you ever tried Screen Hero? We use that from time to time here and it works nicely.

screenhero is great too, no video, but it has voice

Hangouts are pretty good at this. We use them in groups, at least.

I think that team viewer works really well. But then again my company is MS centric so we use Lync and/or WebEx.

A great combination is Skype + join.me

tried gotoMeeting?