What's the difference between the two? Is one of them better to used when backing up DVDs than the other?
Maybe this may shed some light for you: http://forums.afterdawn.com/thread_view.cfm/499156 Hope it provides the answers you were looking for.
and here is another view of +Rs compared to -Rs: http://www.cdfreaks.com/reviews/Why-DVDRW-is-superior-to-DVD-RW/