The main thing I like about AquaMail are the visual customizations for the message list. They are virtually infinite, and I like my "design". But I suppose I could get used to something like FairEmail.
Re: the AM message list, same here. I actually moved away from FairEmail because I got tired of fighting the interface and slogging through the cumbersome/confusing menus to try to customize things. Plus the FairEmail dev (it's just one guy) is way too defensive and snarky for my taste.
I moved away from FE a couple of years ago, but when I was still with it, there were multiple complaints in the Play Store about the app's UX, and he would always try to gaslight users by telling them they just didn't get it or they weren't patient enough or some other excuse. I ended up having a brief back-and-forth with him on a UX issue, and he gave me some BS about how he consulted with UX experts who said the app was just about perfect. I've been working in UX for almost 25 years – FE is
not just about perfect. 😄