If your laptop is used as more of a desktop, a external 5.25(Needs its own power) inch DVD drive will be faster(and in most cases quiet at dvd watching speeds) then another internal drive. Not a good option if you use it for portability however.
I say this as someone a slim laptop drive in my media center(they tend to be louder The Sony is my quietest(DVD/CD, loud for DATA) so far[laptop drive]. my Lite-on is louder. My LG external 5.25, nice and quiet