Office 365 vs Google Apps for Business
The main difference between Office 365 and Google Apps for Business is the maturity of the Microsoft product.
Combine this with the fact that Google Apps for Business is considered by many to be more of a consumer grade product than a business class product and that almost across the board the capabilities are more advanced in the Microsoft Office 365 products than in their Google Apps counterparts.
This is however all subject to opinion and you could listen to IT pros arguing the Office 365 and Google Apps for Business point back and forth for hours without coming to agreement.
Google’s App products are a little cheaper but you pay for them by giving a little of something else, privacy.
Google apps is entirely web based and so you do not get to install the apps on your PC so that you can work offline. Microsoft Office 365 provides both options.
Most people have used Microsoft Office and so are familiar with the Office product suite. This could be considered an advantage.
On the other hand, Google apps are simpler with a smaller feature set and so could be easier to learn to use.