I’ve found that MS Outlook handles tables and embedded rich content better than other clients. I used Airmail for a year and it used to drive me up the wall because it would paste Excel tables as images. I know it’s since expanded support but still on my last trial it messed up formatting.
I also have less sync issues with my non-Exchange server, and I think search is pretty powerful, I heavily rely on custom smart folders.
I miss the quick filtering functionality of Airmail and the abolity to snooze, but happy with the trade off compared to what I get from Outlook.
On iOS, the additional functionality such as identifying people not in your contacts based on email signatures and also the ability to quickly add people from incoming emails via Siri suggestions are all important to me. When I used Airmail on my phone the unknown caller guessing did not work as well because mail did not sync the accounts in the background if not opened.
As someone who lives in his inbox with an average 250-300 emails daily (company email only!), I’ve come to the conclusion that at the end of the day there is no magic email client. To me, the idea is not to have the email client with the most bells and whistles, but rather to use the email client that will help me get through my mail as efficiently and quickly as possible.