Office 365 vs. Google Apps: The bottom lineThe two packages are neck-and-neck in the ratings, but they're completely different in real life. Google Apps is small and easily administered; it covers the high points; and it doesn't try to reach into the more obscure corners of your company or organization.
Office 365, on the other hand, offers the best (and most complex) enterprise support in the business. I'm continually amazed at how well Microsoft has built out Office 365, rolling feature upon feature into the mix, yet keeping the whole package remarkably stable, usable, and manageable.
For large enterprises with strict data controls and complex, diverse operations, Office 365 has no equal. For any organization with less-stringent requirements and a willingness to part with companywide Office document compatibility, Google Apps offers a good, inexpensive, and reliable alternative.
If you're looking at Office 365 and Google Apps for your small business and you don't have a pressing need for Office doc compatibility or a tied-down security requirement, pull out your calculator (or your Google Sheet) and do the math. On the Google side, you have $50 per year per person, plus the price of the necessary copies of Office (rent or buy). On the Microsoft side, Office 365 will run $150 per person per year for up to 25 users, or $180 per person for up to 300 users -- $240 per seat to get all of the bells and whistles.
I bet you'll find that, for most small and midsize businesses, Google Apps is considerably cheaper -- but it may not do what you need to do. There's a reason why Office 365 is doing well in large enterprises.
Both good value, both very different. Take your time to evaluate which is best for your organisation.