For me personally, I like to add all the flavors to my beer from the beginning, not at the end during bottling. Besides, the contribution from DME will be very "diluted" when you add it to 5 gallons of beer. DME supposedly gives you better head retention and also contains additional unfermentables that contribute to head retention and mouthfeel...but I personally can't really tell much of a difference. So as a general rule I use corn sugar for priming (3/4 cup). Here is a great article from BYO that goes into a little more detail.
Priming is the addition of additional fermentables to the beer immediately prior to bottling. This addition gives the yeast "food" for carbonation.
Marc.