I don't like the two moving stages (Rumble Falls and Mushroomy kingdom), simply because you spend more time running and jumping, than actually fighting. I don't like any of the retro-style stages either (Mario Bros., 75 M and Flat Zone 2). These levels are very big and dull (visually and in terms of gameplay), and result in way to many random KO's. And though I don't hate New Pork City, Pictochat or Hanembow, have removed them from the Random Stage Select. As with the retro-stages, I feel they are too big and plain and random.
On the other, I adore the other 20+ Brawl stages. They're simple, but effective; not to mention they are all beautifully rendered and set to a roaring soundtrack. I think their are a lot more killer stages in Brawl than in Melee. That is to say, I omitted more stages in Melee than Brawl, because I enjoy the current stages a lot more. And they feel more well-balanced.