Haven't used Mox yet but Chasquid is great if you want something that's focused on being a streamlined modern MTA rather than "all-in-one". So kind of the opposite of the Mox approach.
I like Chasquid for its straightforward codebase and the hook system that you can use to customize it further.
Stalwart seems to be more ahead feature-wise. As a Stalwart user I will definitely keep an eye on this project. Just a couple of missing features that are a dealbreaker. One of them is also absent in Stalwart - aliases to external accounts.
