Who would win? Lord Voldemort or James the creepy stalker vampire dude from Twil*ght? ^_^?

Voldemort. No matter how fast you are, it doesn't compare anything to magic; especially since if you're a wizard you can most likely create a shield around you. Besides, even if Voldemort did get bit by James, he could still heal himself or have his minions do it for him. Plus James would also have to go through all of the Death Eaters and destroy all of the Horcruxes first before he can even THINK of getting close to Voldemort.