I’ve always use the ‘files with fewer tabbles’ sort. A life-saver since I dump files from the thumb drive into a couple folders daily. Created a folder tabbles pointing to my incoming directories, sort by fewer tabbles (files with NO tabbles are at the top of the list. 🙂 ), and away I go. Been doing it this way since before we got rules, so no rule required… LOL
If you want to pull multiple folders into one file window though… I guess you could create rules for each folder that assigns a "new" or "categorize me" tabble to new files. Once you categorize them you unlink the "new" tabble. (The new link/unlink panel coming will make it easier 😉 )
If you’re just dealing with one directory then a folder tabble should do the trick just fine.