After using Hangouts for years now, I've become sick and tired of it, and have finally found an alternative. Unfortunately, this is only for the text/image chat functionality, but it's a very good replacement:
https://telegram.org/
It was on the front page of Hacker News just a couple of days ago, and that's where I found out about it. Much nicer clients, open protocol (so you can even make your own clients), reliable, and many more features than Hangouts make this a much better alternative.
For voice and video, however, I haven't found a good alternative that is easily accessible to people that don't want to set things up on their computer. Hangouts will just randomly not work for me, depending entirely on random chance, and I still can't find anything more convenient than it.
I like Zoom (http://zoom.us/). I used to use Hangouts, but it consumed a lot of CPU. The free Zoom account allows you to have up to fifty people in a room for forty minutes, or an unlimited length call with just two participants.
I've used zoom.us quite a bit and was family impressed. There's also appear.in which is not as good, but doesn't have all the restrictions the free zoom.us tier has.
I just encountered Zoom this week! I had a conference with a German (I'm in Vietnam at the moment) and she sent me a link to it. I'd never heard of it and was a bit frustrated to need to install another plugin.
But it was a great experience compared to Hangouts! The connection quality was on par with Skype and it was super light-weight for something based in the browser.
What good alternatives are there to Hangouts? Preferably something that doesn't require flaky browser plugins.