From what i have read and experienced in my day to day use of GA, my best bet would be Google. Not because I love and use Google everyday but for me, it works. It offers a suite of services that are easy to use anywhere, anytime. My biggest feature I admire is online document collaboration. You can chat(text or do a hangout) and work on a document in real time. Plus it's spam filter works. And it works well on any device out there. You also get the tried and tested 99.999999% up time from them.
With M$365, some features/services don't work well without their software running on your desktop. Which means you need to spend more to make it work well for you in the long run. Will not run well on most devices and yes the cost factor comes in well when you deal with M$. And you have to wait for their updates cycle to get new releases/versions whereas with GA, they seamlessly update your platform without any much administration.
M$ has a "comom" UI for most users out there hence it will appeal to them but GA is very cost effective. It was free for 10 people till last week. The $50 per user per year still beats M$ anytime no matter how you run the pricing structure for your business. (http://www.microsoft.com/en-us/office365/compare-plans.aspx