The best can either be read as the most elite, or the most productive.
Most elite. Probably the Falcons or the Broncos
But most productive, I would put the Colts in there as well. Reggie Wayne, an impressive slot burner in TY Hilton, and Darrius Heyward-Bey who is purpose built for their West Coast Offense. Adding in the TEs, that's hard to ignore.