Actually it depends on if they bite int the coritid artery or the Jugular Vein. As you may know, biting into an artery can cause blood to shoot out 6 to 10 feet from the neck. Having actually worked in an emergency room I can offer first hand knowledge and attest to the truth of this assertion. On the other hand, biting into the vein causes a slow seep to accrue and that can be easily lapped up from the surface of the neck. In the end, biting into the artery would be a bit like biting into a water blood, you are going to make a mess and blood is going to go flying everywhere. A decent analogy for biting into a neck can be drawn by comparing the human neck to an apple. Biting into a nice juicy crisp apple is like biting into an artery. You bet that rush of rich fresh flavor and of course the juice sprays about dripping down your chin and spraying your face. Biting into the vein is more like biting into a soggy apple. There is no crunch, no spray, and just a slow ooze of juice; still sweet and filling but it is always the fresh bites we remember.
Hope this helps.
On a side note. Vampires are the wimpiest monsters ever invented. Afraid of crosses, sunlight, garlic and blessed water of all things. What a joke! How anyone could ever fear a vampire is beyond me. Stupid, stupid, stupid monster.