I'm workign in TV news now, and have worked with many of the majors over the past few years. There is not a universal winner.
Skype does remain extremely popular because of it's ubiquity and it's fantastic ability to handle very crappy connections. It's not the best when you have plenty of bandwidth, but it's certainly the best when you don't. CNN takes live shots to air off Skype regularly.
That said, if you are willing to pay, Vidyo is doing some decent stuff. I know of at least 3 'radio shows on tv' that operate over Vidyo, with cameras at the radio studios, and the broadcast control room hundreds if not thousands of miles away. I'm not sure about linux support, but there is a free client for OSX and Windows, so any interviewee can download it and join right up using whatever webcam is available.
I'd recommend not looking for a single solution to rule them all. Instead, try and schedule about 10min at the beginning to see what you can get working - start w/ a high end, like Vidyo, if it's struggling or they can't get ti going, try facetime, still no love, step down to Skype.
That is, frankly, what the pros are doing.