Toast Or Roast: Ben Smith
I learned how to blog from reading Andrew. He basically created the model that I try to follow: The incremental pursuit of a handful of threads and arguments over months and years; the insistence on writing for the smartest reader, not the dumbest; the direct engagement with readers and what readers find interesting; and the willingness to include opposing views and even totally change one's mind. I disagree with him frequently, and always have, but haven't ever stopped reading.
Read Ben at his eponymous Politico blog.