I like it the best too but it's also the most underdeveloped/underfeatured app for how long its been on the market (longer than Spark, Airmail, Easilydo Email, etc).
It still doesnt even sync the drafts folder for heck's sake (even the stock Mail app started doing that in what 2009?)! You cant search the calendar, you can't add or delete contacts, on gmail you cannot search back beyond I believe its 25 or 50 entries (they simply use the gmail API, no server search), not HTML email signatures, no in-app browser like every other mail app offers as an option.
There are just WAY too many quirks and the basics missing to use it as a DD for me. And they dont even listen to us developers/beta testers they picked out. Im not sure why they picked beta testers and don't bother listening to any feedback.
There is also a TON of user feedback/votes for features we beta testers mirror sitting there for 1 or 2 years now not acted upon; some with 20,000 people asking for it and the top voted ones. MS is just baffling. They could have a REALLY good app if they just added some really basic things (sync drafts, in app browser, search calendar, edit contacts) people have been asking for since it was Accompli; not even power user stuff