Got this coming up myself soon. My car has full VW history, and I'm going to approach them soon for a warranty claim on the wings, so I think after adding things up in my case it might be worth going to VW again.
It's true that casual buyers like the sound of full dealer history. And I want as strong a case as I can build regarding the warranty claim.
After that, assuming the wings get sorted, I'll probably use Statller. Anyone who knows anything will know that a service there is every bit as good, if not better than VW.
If your service book is fully stamped up by VW there's justification for sticking with them. It'll appeal to more buyers. Otherwise, find a good specialist.