We choose Missive for now because Missive feels like a proper snappy desktop app and is vastly cheaper ($15 vs $50 per user). Front feels like a bloated website wrapped in Electron.
But, Missive is full of design flaws. They seem to add feature after feature without taking the relation between different features into account, nor do they seem to have a UX designer on the team. The Snooze shortcut for example opens a different snooze selector in a private email compared to a team email. The list of quirks goes on.
I fear that we will eventually switch to Front because Missive is unintuitive or (please someone build that) Gmail with collaboration features.
It would be awesome if someone can turn Gmail into a collaboration hub like https://missiveapp.com/ or Front with this SDK.