Hi Ed,(posted 8345 days ago)could it have been the camera lens or did you use the same lens and the same apertures?
If you did perhaps the anser could be found by analysing the motive, seems some films get better separation in the midtones while others get better separation in highlights or shadows. A motive wich is dominated by either shadowdetail, midtones or highlights would probably favor the film that makes the best of that part of the density curve.