I wrote the original post a few days ago when I was just beginning to watch the final half of the final season (5). Welp, having now completed the series I may have to adjust what I said. Frankly the last several episodes of HOW simply didn't didn't measure up. In fact, in retrospect the series never really regained the excellence from its first three seasons. Hence, while I really did enjoy the first few seasons of HOW as much, if not more than any of Deadwood, the latter did continue its excellent quality right up to and including the series conclusion. So all in all, I'd have to rate them fairly evenly - especially since Deadwood had considerably less episodes - and, in fact qualify it by saying that while they were similar in the most obvious ways, they were simply just so very different in many others, making it an apples and oranges debate, to some extent.
But what do I know. I'm just a girl.