We left hipchat for slack for several reasons. First, we saved some money. There were more integrations for slack. The result has been mixed with my more technical users embracing slack, and my less technical users revolting. Hipchat is easier on the eyes and the UI is more intuitive. Both have a long way to go.
There are too many chat clients around and far too many methods to communicate period. Aggregation is badly needed.
Aggregation is badly needed in the whole of technology, but big corporations have all decided that having proprietary cables, closed APIs and locked-in platforms is better for their bottom line than what would be good for the consumer. Also open source/free software advocates are pretty terrible at making cohesive user experiences.
When it was AIM/YIM/MSN, etc, Trillian and Pidgin came in and made the experience usable. Now its Gchat, Telegram, Hipchat and Slack. Some of these have XMPP interfaces (all?) but frankly both companies will keep their APIs as closed as possible because they want to make money on their own platform.
There are too many chat clients around and far too many methods to communicate period. Aggregation is badly needed.