I use both Heartbeat and Slack, and I find Slack much better at helping me avoid missing important notifications or unread messages since they always move up. The “threads” feature is also really helpful, as it allows me to easily keep track of any active thread I’m tagged in or commenting on. In contrast, with Heartbeat (especially as an admin) it often feels like I have to “hunt” around to find missed notifications and DMs, which is frustrating and very time-consuming.