The general rule of thumb is 3/4 cup powdered Dextrose or 1 1/4 oz DME for priming a 5 gallon batch. DME will take longer to carbonate, and while it is true that DME will taste better than dextrose, it's only 3/4 cup we're talking about so the difference it probably not anything noticeable. I don't worry about it so I just use dextrose since it's cheaper and faster. but some people like to stick to the Rheinheinsgebot, so they use DME.
"let me be the first to welcome our new insectile overlords"
On deck: Breakfast stout
Secondary: American Pale Ale
Kegged: Imperial red ale, Breakfast stout, Chipotle Irish red ale, Biermuncher's C3C cream ale