One thing sold me ..
... and that is the issue of data mining contents.
I'm dependent upon my ISP for email service and being rural I'm limited to two providers both of who rely on web based email products, both of whom data mine. Frontier recently forcefully migrated it's customers to Yahoo where, although we retain an "@frontier.com" address, it is simply a mask for a Yahoo address and we are under their TOS which includes the right to scan email contents. My ISP provided email was always designated for financial or highly personal communications while Gmail, and yes one time long ago Yahoo, considered disposable and not used for anything I would consider important. Now that my ISP is defacto Yahoo I feel violated, with results of email content scanning already apparent across the web.
Due to other serious issues with Frontier I'm left with Shentel cable as my sole affordable alternative where they have offloaded their email to Google and Gmail, again to be scanned and data mined. Though I'll more than likely be switching to Shentel seeing as Outlook seems to take this issue seriously I'll be foregoing any "ISP provided" service and going with Outlook as my primary "valued" email account.
It's that simple.
Until such time as I can afford other alternatives such as hosting my own domain and mail, Outlook is will be my mail of choice.
Now if only the Outlook UI wasn't so overly spartan and a bit more customizable I'd be a bit happier ... :/
