Over the years, I have researched and reviewed many articles comparing Google and Microsoft with a view of which one is better and which one to pick, as it relates to the services provided in the "cloud."
For those of you who have heard of the term "cloud computing" or "in the cloud" and are not sure what it means, well ... here is my definition and explanation ... it means that you do not need to purchase and install equipment and install software at your church in order to make it work. Google and Microsoft give you a way to use their products/services that are maintained on their equipment. When companies charge for "cloud computing" these costs are normally yearly fees on a per user basis.
From my experience, after working with both platforms for a few years, the answer is quite clear - pick both! Churches qualify for "free" non-profit use of both platforms. You may start predominantly using one platform but that does not restrict your church from using tools from the other company.
The main choice that your church needs to make is which company you want to use for email. Both are very capable. After that there maybe tools you will want to use from both companies.
If you do choose to use tools from both companies, there is some technical setup work that needs to happen to enable "single sign on" in order to achieve common username and passwords for both platforms.
To make the best decision, it is probably best to discuss with your staff and leaders on priorities and preferences. Next discuss with volunteers and potential contractors if you intend to seek outside assistance during implementation.
In the end, both platforms are very capable and you can't go wrong as both work quite well and with all types of user devices.
Lastly, each company Google and Microsoft do have components that are not provided by the other or as good as the other.