I use both.
Google doc for on the go that I can sync with my tablet. Usually spreadsheets, documents from gmail, sometimes extra files. Google docs is also very useful for sharing files between people, especially shared spreadsheets people can update information or formulas.
Office is used for professional things that need to be turned in and formatted for paper copies.
With android devices, there are a few apps that sync it for you easily -
Google Drive - https://play.google.com/store/apps/details?id=com.google.android.apps.docs&hl=en
Google Docs - comes preinstalled with some stock devices.
