I use K9 it works well, Gmail is not bad either. AM for now unless they remove the basics I use.
I haven't downloaded K9 yet, but I assume it, like FairEmail, can't import existing email accounts, correct?
What do you mean by "import existing email accounts"?
I setup my Fairemail the way I like it and then export the settings so I have a backup if I need to reinstall Fairemail. I think Fairemail and it's many settings is closest to Aqua Mail then K-9. K9 is just way too basic and still lacks a lot of functionality.
What I like about Fairemail (no specific order):
1) quick response time from the developer
2) Can purchase through the Play Store but get the latest updates through GitHub
3) Export and import accounts and settings
4) Hide tracking pixels
5) Best documentation I've ever seen for any email app
6) Notification actions (Mark as read, delete, Spam, etc up to 3 actions can be selected).
7) I don't use this feature but I know it was having all kinds of issues in Aqua Mail but is available in Fairemail, Encryption/decryption supported (OpenPGP and S/MIME).
schedule email to be sent at a later date and time
9) confirm links before opening them (includes ability to select what browser to use)
10) virustotal integration (scan attachments for viruses)
11) ChatGPT integration (I have had recent issues with this but I think it's with the ChatGPT API and not with Fairemail)
12) LanguageTool integration for checking spelling and grammar
And many more settings and features