I'd suggest that while Gmail might cover your basic needs, and certainly integrates well with Android phones, that even though there have been glitches in Microsoft's migration process, the end result of full integration with Microsoft Office, and the flexibilities
it gives (especially for those who use all 3 - Windows Phone, Outlook.com web access AND Microsoft Office) is worth considering.
Of course, if you are using Google apps, why would you bother with Outlook.com? But in my opinion, the finished and integrated product (especially as a Windows Phone user) is an excellent way to manage contacts and groups across those 3 areas, and I extensively
use Microsoft Office, so why wouldn't I want a robust and unifiedcontact manager as part of that. I love having people's phone numbers, email details and addresses at my fingertips wherever I am.
But having lost groups myself in the leadup to the rollover to new outlook.com and wasted a good deal of time cross-checking the restored ones, I still find it very annoying that Microsoft has allowed this to happen.