Specifically curious about Gmail accounts, but as most all email accounts have a web interface, no harm in voting for which one for those.
Being productive in Gmail feels impossible. Even in comparison to the decade old outlook 2007 I feel like I'm in less control.
The interface feels slow. The gui controls are limited, opaque and have all the GUI concessions that only webapps have to have. I don't know if users would ever accept this from a native desktop application, and it's a damn shame that they've still managed enough market-share to kill Thunderbird and turn that into a directionless turd. I don't how I'd ever mange my professional email workload in gmail.
With their interface, emails are something that happen to you and unless you get to click "archive" and never think about 99.9% of then again, it's impossible to keep up.
I bet you would be impressed by the GUI we have built for Missive - https://missiveapp.com/
It’s 100% web, yet it feels just as snappy as the best native clients. We also have a native macOS app that wraps the webview and provides a Dock icon, system notifications and Quick Look (space bar to view attachments).
Work Email: Google Apps Gmail (web)
I used Sparrow in the past (https://en.wikipedia.org/wiki/Sparrow_(email_client)) for a few months until they were acquired by Google. Now some of the features they had were implemented in Gmail and Google Inbox.