So basically the title. Which App is your favorite one and why? I'm still mourning the loss of google's inbox and never found an app that scratched the itch like inbox did...
On desktop I use Spark and on mobile currently google mail, because it got the job done but nothing more.
If you're on Gmail, buy Mimestream for Mac and never look back.
If you're not using Google for your email, and/or you're looking for something on iPhone then it's a tougher choice. I wrote an extensive review of the options not too long ago and landed on Spark, but your priorities may be different from mine. Have a look and see what you think: https://kevinyank.com/posts/email-apps/