My preference is probably steam chat. The new signal desktop is a dumpster fire.
Most people in my age group simply don't spend very much time in front of a computer. Their phone is their portal to the internet and has generally everything they're looking for.
Slack is much better, but Discord sunk its teeth into the gaming community and it spread.
Slack's extra features and integrations are nice, too, but I just don't like Discord because it... doesn't even work as advertised.
Pretty interface, easy to use, voice is pretty low latency (although I miss my mumble server), and it uses ~80mb of ram to sit in like 5 groups, which while not fantastic blows "rather open it in chrome" slack out of the water.
New signal desktop instantly uses 200mb and has to "loading messages" for 3s every single startup :(
On the whole, for a product proudly marketing itself as a Slack replacement, it does a terrible job actually providing the same functionality.