A good dealer...that would be one that gives me the great service locally like the service I receive when I am broken down 1000 miles from home. I find it hard to believe that the best service I have ever received from a Harley dealer was in Rogers, AR when I was broken down. A dealer 1000 miles away, and they not only treated me like gold, they even went so far as to make a follow up call to me to make sure that my bike was running well...knowing that I was back home and 1000 miles away from them.
I don't like it when the service department personnel have a bad attitude, damage my bike, and then lie to me. I don't like it when I take my bike in and get it back with something wrong that wasn't wrong when I took it in. The most recent example wasn't even on my bike, but rather a friend went to pick up his bike on Friday and he made it to the end of their parking lot and realized that he had absolutely no lights on his bike anywhere. How can a dealer give back a bike that wouldn't pass the state inspection anywhere. Anyway, before I start going on and on with examples of pi$$ poor service that I have experienced personally, I'll just answer the original question.
If you can save some money buying the bike at a different dealer, go for it, and then go to the dealer with superior service for any work that needs done on the bike. The dealer should be more than happy to pick up a new customer in the service department regardless of where you purchased the bike. If I really have to pick just one though, I have to go with the superior service as the place to buy. I will never buy another bike from my current dealer because I am so completely dissatisfied with the service I receive there.