Skype - use it daily to communicate with our team. It's free, easy to use, conversations with multiple people is simple, and video/voice works really well.
Skype is good as compared to g talk. Skype offering free video calls and it is providing much good facilitation to its user.
I think Skype is more commonly used. It can be used for professional purposes like an interview. I use Skype more than Google talk. However Google Talk/Hangout allows group calling for free unlike Skype.
I prefer to use skype because it's easier and very much known to even the most common people. Not everyone uses Google (where hangout/talk is found) but almost everyone is familiar with skype.
I use them both for different purposes. Sometimes Skype is called for when quick calls are needed, but Google Talk is great when you need to see all of the people involved, and the plugins are great. I'd say to keep both handy. I enjoy using both in different circumstances.
Skype is beautiful. I've noticed the quality of Skype is above and beyond everything I've seen. The international calling is a plus as well