We asked the same question a while ago where we were choosing a communication platform for LUNADIO Comunity.
We let our newsletter subscribers vote what they want to use, and they preferred Discord over Slack.
I like both. There are pros and cons for each platform.
Everyone has Slack installed already, and they got great onboarding.
Discord has voice channels, unlimited message archive but missing threads.
For work, I prefer slack. It has a lot of functionalities tailored to a team-based collaboration system. While I prefer Discord whenever I am with my friends, it has this vibe that makes you want to chill and talk with them.