I do agree that dealer experience is a major factor.
I had Nissans for a few years and had bad service generally, just before I got rid of the last one I found a dealer that gave great service.
Then on to Volvo, generally poor experience for me although in fairness it never really went wrong.
Next came Mercedes which was dreadful and the thing was constantly going wrong.
Renault Manchester have been spot on so far so I can't really complain.
With the Porsche I use an independent rather than official Porsche Centre who are fantastic, I have heard some bad news stories about some Porsche main dealers though.