I have only ever read the Wheel of Time by Sanderson, but the dialogue was enough to convince me I never needed to bother with him again. Meanwhile, I find King to be probably the best American English writer that I've encountered. By that I'm really only talking about his use of the language, and what a pleasure it is to read. And of course, dialogue is a part of that. This is all subjective of course - that's just how I feel about it.