"Favorite"--especially when applied to people--is, I think, problematic. And in the case of Queen Victoria . . . well, she had a number of grandchildren, and during a period that spanned decades was closer to this one or that one for various reasons, including birth order, parentage, proximity, personality, physcial attractiveness, and neediness. So perhaps "favored" would be the better term? In that case, I would certainly agree that firstboarn grandson Wilhelm was a favorite, as would be the children of Beatrice and those of Alice.