Airmail is the new gold standard!
I have used Airmail for a long time and have tried serveral other but always found something I did not like and came back to Airmail. It is now my new gold standard. And Sarah in Tech Support is Awesome!!! She helped me figure out how to change the notification sounds so that they are less annoying.
pst4r about
Airmail - Your Mail With You, v1.6.4