Slack was great to use, but not sure if I'd choose it over Discord for every situation. Slack doesn't have VOIP, but it seems easier to restrict users coming into the channels by default ( something I haven't really tested much on Discord ). I'd say I prefer Slack's notification system a bit more than Discord's default setup as it would display who messaged me and if it was a general announcement or a specific mention without me having to tab over to Slack to view it.
I'll be using it for the next few months at least so I'll try and get a better comparison of the two for the future. I do know that if a team explicitly doesn't need VOIP and prefer's Slack's layout I could see it being a clear winner.