I love playing tug of war with my dog. This is partially because he didn't show interest in toys at all early on, and getting him to actually pay attention to a tug rope was a long and often unrewarding process. Thankfully, he is now always excited to have a quick game of tug with me.
I am confused about who should be winning this game. On the one hand, I've read (for example, here) that you should always let the dog win, because it sates their natural prey drive, and encourages them to look to their owner for help in relieving aggression or anxiety.
On the other hand, numerous sources (The Dog Whisperer, for example) say you should never let the dog win, especially if the dog is a dominant breed (bull terrier, ...), because they need to recognize you as the alpha, etc.
So my question is, which is it? I suppose it depends on the dog and its temperament, why we're playing, etc., but I am interested in any pertinent information.
I request no anecdotal answers. I am only interested in scientific reasoning (or lack thereof) behind the claims above.