I've read a few of King's novels and compilations, but by no means all of them.
My favourites would have to be IT and The Stand. I also enjoyed Needful Things, Pet Cemetery, The Long Walk and The Dome (it has a surprising and Interesting reference to Lee Child's Jack Reacher character).
I just couldn't like Salem's Lot - I wanted to, it was a good premise, but in the end I didn't enjoy it. One of many books I expected to like by the glowing reviews, but did not - for one reason or another. (For example, in sci-fi, I didn't like Farenheit 451 or Slaughterhouse Five - which would put me in the minority, I would assume, of science fiction fans.)
Some people have suggested that King struggles with the novel format and should stick to short stories. I wouldn't go that far but, after reading a few of his collections of short stories, I'd say they might have a slight point. Some of his best writing is found there, or at least some of his best unadulterated prose, undiluted by less refined fare - like filler content, gratuitous descriptive asides, parochial genealogies or back-stories and other such unnecessary expository passages (or should that be pages!)