Mattermost is currently a better UX with a more stable codebase, but I suspect that the Matrix/Riot federated model will one day overtake Mattermost. Personall

Mattermost is currently a better UX with a more stable codebase, but I suspect that the Matrix/Riot federated model will one day overtake Mattermost. Personally I use Mattermost at work and Matrix/Riot for personal chat. If Matrix/Riot began to overtake Mattermost in terms of UX, we would probably replace Mattermost with Matrix/Riot at work.