The major benefit of slack over hipchat is slack comes with integrations by default. IE: instead of having to use Zapier or such to hook into Trello slack can h

The major benefit of slack over hipchat is slack comes with integrations by default. IE: instead of having to use Zapier or such to hook into Trello slack can handle it for you. HipChat only has an API you push to, whereas Slack can pull from other services. We tried it and kept with HipChat. I found Slack's interface/text to be less readable than HipChat. It might look better, but for reading information and usability HipChat won. Our entire team is happy with our choice.