I'll pressume it was a giant accident that you left off Da Ali G Show and Curb Your Enthusiasm.
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Where I am, I don't get to see every HBO show, but I'd imagine Deadwood is the one I'd like the most if given the chance. I also haven't seen Carnivale or Entourage. I could never get into Six Feet Under and The Sopranos has always impressed me everytime I've gotten a chance to see it. But despite my limited exposure to the channel, I've loved everything about Ali G and Curb.