In short, the "unofficial" icons.
From my experience as a user, the "unofficial" approach is the most common (examples: Google Drive, OneDrive). In addition to this, there are a number of problems with the "official" approach, which is solved using the "unofficial" approach:
- Lack of internal consistency, as you mention
- Copyright problem
- Have to keep up with the ever-changing icons apps
- And what to do with generic files, such as JPEG, AVI, TXT?
The big advantage of the "official" approach is that the user can recognize a file type faster, but I do not think it overrides the issues.