I have both Campbell's (4 definite Campbell males) and Winter Whites (2 males, 2 females) - as well as a few suspected hybrids so I guess I'm probably in a reasonably good position to have a guess at working out the difference.
For me, the biggest difference I see (ignoring the obviously physical) between Campbell's and Winter Whites is in terms of personality. Winter Whites are quite soppy and easily affectionate (or maybe its just the way those little eyes look so soulful?) whereas I find Campbell's make your work for that affection a lot more - it comes across that they quite clearly think that you're there to satify
their needs (there's only one master of a Campbell, and believe me, it isn't you!) Their personalities seem much more distinct/extreme than WWs. My Campbell's make it
very clear when they're not happy with what I'm doing and specialise in throwing strops better than I've ever seen any hamster do. They've mastered the art of how to be appear truly offended. But, once they've been won over (or - in their eyes - you've been fully trained up), I find them soppier than any WW.
Which leads me to why I suspect my Flower Girls of being hybrids. Apart from a few physical characteristics which make me think hmmm, there's WW in here somewhere, they are so curious and friendly with not a strop in sight, there's no way that they can be pure Campbell!!
So here's my rule: Campbell stroppy, WW soppy.
And if I had to make a choice? I'd have to go Campbell, purely because I adore my Campbell Jason so much. We've been together 9 months now and he's like my little puppy dog (but who sits on my shoulder and whispers in my ear), I don't think he's actually a hamster at all! (but if you ask him what he thinks, he'll probably tell you that I've completed my training and I'm giving him the right kind of treatment).