I used Google Drive for about 5 minutes then went back to Dropbox and haven't looked back. Firstly, finding where the hell the Google drive folder was located was a pain - then discovering it's odd internal hierarchy and the fact that trying to open files in there launched Google Docs rather than the local application default drove me mad.
Dropbox gives me exactly what I want and need: a simple folder that does sync across all my devices and opens files using the local default application.