Google Drive can sync documents on multiple machines and in the cloud. If a Google document is edited offline, there's a potential for conflict with other editors, and again if users apply Word formatting that isn't yet supported by Google. If there are no conflicts, the document syncs automatically. Otherwise, either a brand-new document is created with the changes, or you can choose which changes to use.
Microsoft Office 365 shares Google's synchronization problem when documents are edited locally. The Word Web App that comes with Office 365 has a bit less functionality--in addition to the real estate--hogging "ribbon" interface. But, most important, it lacks auto-save and what-you-see-is-what-you-get.
Also, unlike Google, the Word Web App attempts to maintain a level of compatibility with the standard desktop version of Word, but it can't yet display all the formats. Say, for example, that you have white letters on a dark background. It looks fine when first uploaded and viewed in the Reading View. But click on Editing View, and the résumé sections are immediately misaligned, formatting commands butt into the text, and background colors all disappear. To make sure the edits look right, you'll need to switch back to the Reading View.
Editing the same sample résumé in Google is an easier matter, as this image shows:
With Microsoft's Word Web App, trying to edit the same document from multiple locations is difficult since changes are not saved in real time. There's a complex process of locking, unlocking, and reconciling files if multiple people edited them at once. If your employees need to do any serious editing, they'll need to use the desktop version of Word 2013, available within pricier Office 365 subscriptions. (Collaborative editing in Word 2013 works only with the step-up Office 365 plans that add SharePoint.)
Microsoft's mobile functionality is in place only if you're using the well-built Office apps for Windows Phone 8, or if you've paid for Office desktop software for a Windows 8 tablet. There are no iOS or Android apps for Office 365, though third-party apps let you edit Office documents. Google, on the other hand, offers free apps for iOS and Android, but not for Windows mobile devices.
Winner: Google Apps wins. Microsoft's Word Web App isn't ready for prime time.