Believe you me, I tried them all.
Actually, the only email client that sucked the least of them all was Microsoft Outlook. I’d never believe I’d admit it while sober, but here I am.
Now it looks like your email provider’s webmail is not that bad, unless it’s some sort of imap client on server (RoundCube, for example). It efficiently delivers a view into your whole mailbox without downloading the whole thing. Search works better. You define your email rules and they work at the source.
Dunno, man, the world sucks in general, and the world of email in particular.