Google Hangouts and others are good if you can guarantee that all users have accounts and are logged into them. This can cause a great deal of confusion at the beginning of courses no matter how well documented the process is.
I recommend either using a service which has a dedicated plugin in Moodle, e.g. BigBlueButton, or a service that doesn't need users to login, e.g. http://blog.matbury.com/2014/09/02/instant-simple-video-conferencing-free/ (limited to 8 users per group) and https://moodle.org/plugins/view/mod_webrtcexperiments
Both the latter examples use an open, peer-to-peer (like Skype but with no need for plugins) web conferencing protocol called WebRTC: http://www.webrtc.org/ This does away with the need to rent or install expensive and complicated media servers.
I hope this helps!
