The biggest consideration as to which format you use will be whether your burner is single or dual format and the preference of the players you'll be playing the copies on. You can check player compatibility here: http://www.videohelp.com/dvdplayers _X_X_X_X_X_[small] JMLS-166S/Plextor PX-708A/Plextor Premium[/small]
When I started backing up movies my first software was DVD X Copy and my impression was that it tended to favour the +R media, but then again, it may have been the NEC1300a I was using.
