Have you used both?

Hipchat was basically unusable for me. Constant crashes, sloppy integrations, poor search, and a notification system that did more harm than good.

Slack is completely different. Pre built integrations mean I don't have to spend time writing a bot. Starred search means I can find that message from a few months ago with the click of a button. Auto responses mean I can inject some humor into conversations during the work day. Image comments mean I can use slack to gain feedback on wireframes. I could go on but theses are just some of the things that make slack far better than Hipchat.

I use hipchat at my place of work. It has so many issues. People appearing offline at least every other day when they aren't. Auto reconnect may have never worked even once for me that I can recall. Even worse, when trying to auto-reconnect and it's not reconnecting, the only thing you can do is close the app and open it again.

From what I understand, Slack came out of the gate with integration with a bunch of other apps, whereas Hipchat had to play catch up on that front.

HipChat can't handle multiple accounts, making it almost completely unusable if you belong to more than one team.

Or Kato