We migrated from IRC to Mattermost and haven't looked back. It integrates so well with our Gitlab/Jenkins flow, too. It's been great.
The biggest benefits for us:
- Easy to use web push endpoints w/ API keys (great for scripting with curl)
- Integration with Gitlab / Jenkins
- Chat Logs (see what happened while you were away)
- Public listing of channels (no more "oh you have to join #whatever to see that")
- Mobile Web App (I can't get the Android app to work with our self signed cert, but that's OK).