I initially went with Mailbox and stuck with it even though updates have slowed to a trickle because I was hooked to the triage features. I then went to Spark because it is essentially a better Mailbox.
I can't use inbox because it doesn't have permission to access my work gmail account, and cloudmagic feels too slow and laggy for me.
I am trying Outlook now because it somehow seems to sport a more polished interface, and it has an iPad app (something which Spark still lacks). I have been wanting to move away from Mailbox for a while, but simply haven't found a better desktop mail app that supports push gmail, and as far as possible, I would like the same email client on all my Apple devices.
I was looking to replace the native mail app on my phone about a month ago, but decided to just stick with it for the time being. I did really like Outlook a lot when I tried it out. Spark is also very good as well. But I generally just receive newsletter emails from places I shop and/or travel promotions from airlines/hotels, etc. So I can't say that I coorespond with people through my personal email all that often.
IMO, none of the new back of email apps "have it all".
I am currently settling with Inbox by Gmail. However, I am missing the "share sheet" and Google Drive support.
The Gmail app has the functionality I need but it looks outdated, and is a bit of a pain to use on a 6s plus (e.g. no support for Apple's "swipe to go backward" gesture.
Boxer is very close but (IMO) performance is poor when you zoom emails.
Outlook is also very close but (IMO) its landscape view on the 6s/6 Plus is poor when compared to stock Mail. It lacks zoom in landscape mode and wastes space (e.g. the composition and view panes are a microscopic fraction of the screen).
I am looking forward to see what the forthcoming Airmail IOS brings.