I don't think we'll ever have a "best of both worlds" Doug. I've used Gmail since the week it launched the first beta in 2004, and it's always been a bit of a love-hate relationship for me (mostly love). With the demise of the Google Notifier for Mac, I went with Mailplane, but even it has problems. Like when I see my iPhone update with new mail and I'm looking at Mailplane and it won't update at times with even a forced refresh. I often have to close/reopen it to see new messages. But, it's hard to live without my Google Calendar only a tab click away, one of the primary reasons I use Mailplane, that plus changing view zoom sticks with Mailplane and won't with Gmail.
For years I've thought Gmail labels were the perfect filing solution, but over the past few weeks I've been analyzing just how much I really use that feature, and for me...it's not all that much. I think I could simplify my life by putting everything into appropriate folders (as in all other email apps). Apple doesn't realize just how much money they're losing by not allowing people to use private domains with iCloud mail...which I would do in a heartbeat just because it would work perfectly with Mail.app. I would pay even more than I currently pay Google for this solution with Google Apps Business. So, I'm actually on the verge of moving my private domain to the best email service I can find and then using it with Mail.app. The problem here, of course, is I'll lose the best spam control on the planet (Gmail). So, as you say, there simply is not a "best" solution for all these things. I'll at least try a new email service first with some other domain to see how I like it before moving my primary email.
Lastly, the other thing that incenses me is synching of flags between iOS and Apple Mail. It works fine between Gmail and iOS Mail, since all I care about is whether a message is starred/flagged or not. But using Apple Mail, when I flag a message it will not show as flagged in their own iOS Mail, which is incomprehensible, given they built both apps.
If you find a great solution or discover anything new...please post it here, Doug. Thanks.