I've gone a little nutty with EMail apps. I've got GMail, GMail Inbox (which I still haven't really figured out yet, Newton Mail, Outlook, my Native LG mail app.
Newton mail & Outlook have pretty much become my two go to apps (my office email is office365). I use Todoist & Evernote pretty heavily, and really prefer to process my email when I read it (i.e. decide what to do with it, and file it away with a task or dump it into my reference files in Evernote. Occasionally, I'll drop a long newsletter or article I want to read later into Instapaper. Newton allows all three, so I can use a very similar system on my mobile. Newton also just released a Windows 10 desktop I just started trying out. Newton also has a Sanebox type of filtering system that dumps newsletters, marketing and some other junk type emails into a "less important" (I think it's called) folder that you can scan at your leisure, similar to Google's categories. Newton's calendars and custom themes are weak also.
Outlook looks great, and is the most reliable with my work calendar and ties in with some other Office stuff nicely. They just released optional integration's, the only one I use is Evernote, no Todoist. When Todoist gets around to writing the integration for Outlook mobile, it'll be perfect for work email. The focused Inbox does a good job keeping junk out of view, but it's still there when you go to your desktop.
Gmail's a great email app, but I found that it was becoming a pain to switch around to the different categories (updates, Promotions, etc and they aren't doing such a great job classifying emails. I have it set to only notify on the Primary inbox, so there's a lot of stuff I don't see unless I go hunting for it or until I'm at a PC. Still by far the best search for finding stuff on the go.
All can keep all of your calendars (I have like 10 in GMail alone), and let you hide/show individual calendars. All can have Unified or separate inboxes. The thing I want most for these are seperate inbox icons with unread counts for each inbox. Closest I've found is a widget from Newton that has three buttons, Unread, Search and Compose, but the button can't be seperated and all three take up too much space.
Newton seems really expensive, and they'll give you a whole schtick about how it really isn't since you get all these features you would have seperate services for (like Sanebox), but when you put it the perspective that it's cross platform now (you get the Android, iPhone, iPad, Mac & Windows 10 apps), it really seems a lot more reasonable.
If you're willing to pay, Newton's great. If not, Outlook's pretty good. As with any paid app or trial, try the trial, let it expire and you just might get a discount offer to come back....
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