both will work, just depends on color changes you may want/not want, if you have a dark beer, DME would be fine, but lighter colored beers maybe light is best, but again, that's going to be only a VERY slight color change for priming. Other than that I don't think there's any difference.
It shouldn't matter much either way but I would stick with what you used for fermenting. This will keep the flavor and color the same. They will both work just fine for priming, its just a color/flavor thing.
The amount of DME you add for priming purposes is so small I wouldn't worry much about any color or flavor addition. Of course, use sense; Dark DME in a Pilsner might have an effect.