For more than a year, I have been trying almost every non-Apple mail app for the Mac and for iOS. In that process I have found some great Mac alternatives as well as sever iOS e-mail apps I really like. However, I have always wished for a unified experience. Something that is feature compliant between desktop and iOS and has features to to help me get my inbox to zero daily.
I may have finally found e-mail nirvana with the release of Mail Pilot 2 for the Mac. ( it is actually in Public Previw right now and you can get a trial copy for free here ) They added many new features with Mail Pilot 2 for iOS, but without a desktop version that took advantage of the "set aside" and "reminder" options, I only found it frustrating to be switching between differing desktop and mobile apps.
If you are someone who deals with a lot of email daily, I highly recommend you take a look at Mail Pilot for both Mac and iOS. In just over a week of testing out the beta, I am convinced I am already processing email much faster and am able to keep my inbox under control in a way that no other apps were able to help me achieve.