Complete action using When I click on a doc file it directly opens with OfficeSuitePro. I don’t anymore have the choice between OfficeSuitePro and QuickOffice because once I have replied Always to the message: Complete action using” that gave me initially the choice.
This happens for my files stored in DropBox and GoogleDrive.
I went to the apps settings to try to clear the default but found out that there were no defaults set therefore the clear default button is greyed.  I uninstalled and reinstalled the apps but the problem persists.
If you've tried to clear it from the apps settings for Dropbox and Google Drive, you'll find there are no defaults set, because the default is set with the app that opens the file, not the app you open it from. From Apps in the device settings, go to Office Suite Pro's settings, and click Clear defaults there.