I use drive now, moved from Dropbox a while back. Both are good, I have 2 desktop PC's, two laptops and two phones that I keep synced with them. Google Docs has now merged with and become Google Drive.
The app on my SGS2 allows me to edit both MSOffice spreadsheets I've created on my PC along with the google docs spreadsheets. On a mobile device it won't automatically 'download' all of your files, just file listings, so when you want to access each file you download it at that point.
It's just easier for me having google contain everything I need, contacts, calendar, documents etc. That was the main reason I moved from dropbox.