I have to agree with Kate. Pratchett would be my first choice. I've talked to more people, young and old alike, who have returned to reading the genre because of him. I also agree that Dave and Sarah are two writers who are under-appreciated and yet who have great talent and engaging voices.

Of the others, I have to take my hat off to Rowling. She put forth a product that made kids -- and adults -- want to read. She brought a number of readers to the genre who had either never considered reading SF/F or who had left the genre and had no intention of ever returning. For that, kudos.