I've worked in one office that had Skype (for business) properly integrated, and it was very nice. But, like so many other things, they couldn't just fix bugs, and make sure to keep it working on new OS versions.
I am not affiliated, I just like it.
I do like mumble and ran my own server for years, but client wise it is not as easy.
These should be added soon™, though.
What we need for the internal communication (within the company) is a simple IM, integrated with ticketing system (a bunch of generic rooms, per-ticket rooms, linking from tickets, ...). We're pretty much set on using Mattermost for that, which has the advantage of being self-hosted.
For voice (typically group calls with other engineers) we'll probably stick with Skype for now (I the Android app on my phone for that). For meetings with customers we usually use a regular service with dial-in anyway.
We don't do video, and I don't think I've needed screen sharing in the last few years.
For video though your options are definitely more limited, keep an eye on Riot, I'm not sure that it's ready yet, but when it is it will present an extremely good option. If you only need mobile, Signal does it today and is probably one of the most stable and secure products around, can't vouch for the video quality though personally.
Google Hangouts.
But I guess we don't really need the video calls that much (After all, who'd want to see video of engineers working mostly from home, right?) and the ability to self-host and integrate Mattermost with the issue tracker etc. is quite neat.
Web-based, supports notification, Slack integration, custom urls.
We've been using Skype for internal communication for a very long time. Back then it was the only option that worked on all the OSes we need (Linux, Windows, Mac), had all the features, and it just worked.
But the Electron app is just damn terrible. The message layout is super inefficient - it can display maybe half the messages compared to the native client. If you click somewhere, it un-expectecly moves you somewhere else. And it just stopped delivering new messages some time ago (I've tried to downgrade to 5.2, but that made no difference).
Interestingly enough, the web skype delivers messages just fine (it still sucks for all the other reasons).
And it also does not drain the battery that much. The devs apparently had the bright idea to render the messages window as canvas, and refresh it at 60hz no matter what. Because of emoticons. The web skype does that too, but if the tab is inactive Firefox suspends that.
The only thing that mostly works for me is the Android client. I wonder how they'll break that one.
In any case, we have lost all hope Skype will get better again. Also, there are other options nowadays.