I have to disagree with this one... I still cringe when I recall an experience a couple of years ago with a provider.  She was literally scraping her teeth on my cock, it was brutal (and I would humbly state I am of *average* size- at best, lol).  I had to ask her, no beg her, to stop.  

I will agree that a good blow job - at that moment - is the best blow job I've ever had.  

cheers