My position on this is to calibrate the display first, with the DVD player in teh default mode... With the exception of bad DVD players, this typically results in the ability to achieve excellent results. In some cases, the display will not have the necessary adjustments needed to achieve the desired picture quality, in which case the DVD player can be tweaked to make up the difference.
With this method it is recommended to have the DVD player on a dedicated input, so the picture quality can be adjusted differently (if needed) for other video sources.