[Neithan]

All right, I concede the point, Tulkas was greatest of the Valar in terms of "power" and that is why he could take the greatest hröa. I will point out though that Tulkas is not listed among the 8 chiefs of the Valar, and I don't think that it is because he came late (he could have been added to the list, just as Melkor was taken off it). I think that his low rank had more to do with his lack of knowledge and wisdom.
So then is Huan's spirit greater than Sauron's? Somehow I don't think so, my theory then is that Huan won the fight because it was his fate to live and to fight the other wolf (Melians power could not keep Beren out of Doriath because of his fate).