One of my customers (maybe two of them) use WebEx. They're paying for it but WebEx has a free plan to make a call with up to 3 people. The web client requires Java but a native client was preinstalled into the Samsung tablet I bought 6 months ago. Quality is good. Screen sharing seems to be better than with Skype and Hangout.

By the way, I had too many problems with Hangout so I can't recommend it, even if today I had a four people conversation (audio only) and it was perfectly fine.