Like you, I've tried lots of different mail apps - Mailbox, Sparrow, Airmail. I've enjoyed using Thunderbird, Outlook, Mail. And I've used web interfaces for Gmail, Fastmail, Hotmail, etc.
In the end, which email client I've used has barely made any difference. The key is in processing the emails - forwarding to Evernote for reference, adding to Omnifocus if it's a todo item, replying quickly if I can, or deleting if it's irrelevant.
I found that extra features like tags and snooze just made me more disorganised, instead of less, as I spent more time fiddling with the features and wondering why something had gone wrong.