Which company has better quality control? Nikon, Tamron, Tokina or Sigma?

As a long term Nikon user, I have always relied on the Nikon range as they offer the best lenses IMHO.  However, I do user Sigma lenses where Nikon do not have a lenses with the specs I need. Both are superb lenses,  With Sigma, I always get the DG range as they offer much better results

Happy hunting