Ask 10 people, and you may get at least 8 or 9 answers.
My personal preferences - among those I have tried - are Fiorella's Jack Stack (for burnt ends and for a more upscale 'cue experience in general), Gates (for a killer brisket and sauce) and Oklahoma Joe's, which looks like a converted gas station that now serves amazing BBQ.
FWIW, Fiorella's also has the best BBQ beans I've ever had and a good beer list.