wasup VS runbox7

I've only ever worked at places with self hosted Exchange for e-mail and groupware. As a client, I use Outlook Web Access (OWA) most of the time and I think it's fine. It's simple, feels reasonably snappy to me and I like having the same interface on all the different machines I need to login from. Sometimes, I need to reach for the desktop version of Outlook in a Windows VM to access options or features not accessible in OWA (or in the sluggish abomination that is Outlook for Mac). However, in the end I don't care all that much about my e-mail client because I use a simple inbox-zero-ish approach to e-mail and only really need Inbox and Archive folders (as well as a delete function). This works with every client.

To have an offline archive, I also have Apple Mail connected to my Exchange accounts. I never use the app itself but frequently use Spotlight to search for and preview e-mails. However, if I'm already working in OWA, I use the search function in there. In my experience, it works well and doesn't feel significantly slower than searching locally in my offline archive.

[Sidenote: I find it annoying to have to use Spotlight for local e-mail search instead of Alfred.app (which has been my universal search app for many years). Alas, Apple only allows access to the e-mail folder on MacOS for their own apps for some annoying reason these days.]

Outside of work, I have the same setup with Apple Mail and Spotlight for archival and search. As clients, I use K-9 on Android and Apple Mail or runbox7 on the desktop. The latter is the webmail app of Runbox, my e-mail provider of choice (I think the app is pretty good - and open source on https://github.com/runbox/runbox7 ).

I wouldn't call this the "best" option. "Best" is tied to a specific case, and OP's case isn't clear to me. I've self-hosted my mail for ~5 years, and I moved on to runbox.com now. Not expensive, cheaply hosted with green energy in Norway and their web UI is free software.