My employer has tried Slack and RingCentral for remote development work. We use Slack chat all the time, but RingCentral seems a bit better for screen sharing.

Whatever compression algorithm Slack is using is probably fine for a webcam, but when screen sharing, compression artifacts make the text completely illegible for seconds at a time after scrolling, and even after it has caught up, it's not as clear as RingCentral. We end up using Slack calls a lot because it's well integrated into the chat features, but the compression is a major pain.

On the other hand, I find RingCentral's screen annotation tools kind of awkward to use. They have a variety of options, but you can't select them quickly enough, and opening the palette hides the mute button! And you have to click another button to clear it. Slack only lets you draw on the screen, but you don't have to select a tool and it fades away on its own, which I found a lot easier to use.

I can't really recommend either one, but RingCentral is less bad for screen sharing.

Update (April 2):

Slack video calls seem to have a limit of 15 people. RingCentral can do a lot more.

My employer is becoming concerned about potential security issues in RingCentral and Slack and is looking for alternatives. Candidates include Amazon Chime, Jami, Jitsi, Mattermost, Riot.im, Tox, and Zulip (with Jitsi), but we haven't tried them yet.

I have a bit of a negative answer, in the sense that I don't know what to recommend. A lot of people in my life (colleagues, friends, family) want to stay in touch (and I with them), but each person seems to have their own preferences about software, or at least sufficiently many subgroups of them do that no single tool will suffice. At this point I honestly think that it's not so much the quality of the tool, but more who are already using it, which determines which software is best. If you and your friends all used to meet on Minecraft every Tuesday, then that is probably the ideal way to keep doing things.

As of yet I'm using Skype, WhatsApp (+WhatsApp Web), personal email, two work emails, two Discord clients (one in browser, one as an app, with separate accounts), my phone, two Slack workspaces, weekly Zoom group meetings, Google Talk, MS Teams and the occasional Jitsi call. This is crazy, but all of them are sufficiently low traffic that I don't really mind.

All of them work fine, I do have mild personal preferences (for Slack, Discord and my phone over all the others) but like I said above it's far more relevant to stay in touch at all than to do it with the right tool.

This answer will be addressing the use of software for social life. Recently my extended family has been making use of Zoom to celebrate birthdays, while my friends have been primarily using Discord. Overall, I've found Discord provides a better user experience.

Of the two, Zoom has been comparatively easier to set up and run, however, the audio and visual quality seemed variable while we were using it. Also of note is the multiple security issues that have been raised with Zoom recently. Another advantage of Zoom that I've found is that it seems better able to handle large numbers of participants, as Discord generally starts to slow down and cause connection issues above ~10 people, though your mileage with that may vary as internet speeds are not great in Australia. Zoom also seems to be easier (though not easy) for people less familiar with digital technology to navigate.

The main benefits of Discord are better quality audio and video with under ten users, and the ability to create servers and chats that last for more than one call. From using Discord fairly regularly since before the pandemic began for keeping on contact with friends I haven't seen recently, their servers are fairly stable and the audio quality does not suffer significantly from slow internet connections. The ability to create servers and chats is also very useful for keeping in contact with friends and family, as it means you can organise meetings and chat outside of them in the same place. As a result of sharing a server, I have been able to keep significantly closer to my friends due to the low level of effort required to send a message and ask them about their day or share an interesting video.

To summerise, Zoom seems more appropriate for large meetings, where low-quality audio and visuals is not a game-breaker, and where people who may struggle with navigating user interfaces will be present, whereas Discord is better suited to smaller groups who wish to keep in regular contact easily.

I ended up writing an extensive post about what virtual worlds are best (if you're aiming for something more immersive than a videocall).

The tl;dr is:

1. Town Siempre is best if you want a simple app you can easily invite people to for an informal party. You walk around a teeny pixelated world, able to videochat with people nearby.

2. Minecraft is best if you want a fully featured virtual world to "live" in, and (potentially) if you want to go on "online hikes". 

3. Mozilla Hubs is similar to Town Siempre, but 3D instead of 2D. It has more features, but I found it a bit overwhelming to use.

4. AltspaceVR is like Mozilla Hubs, but requires either VR or Windows. It's a bit more polished and smooth, but higher barrier to entry.