First of all, American heros are cool as hell! However, they get over used to the point where I can't understand which "universe" is which! I mean, there's The Amazing Spider-Man, The Spetacular Spider-Man, Ultimate Spider-Man, The Web of Spider-Man, and soo much more! I don't know what comic line to follow up on! Not only that, if Spider-Man issue 112 ends you have to pick up Iron Man issue 225 in order to see what happends next!
Also, there isn't any action going on in DC or Marvel comics, sure you'll see a punch here and a kick there, but that's about it. It's more about dialect and stuff like that.
Manga however, is easy to follow. It starts, it has a middle, then after many years, it ends. Simple as that. You'll never see, Ultimate Dragon Ball Z, or a remake of Saint Seiya or Sailor Moon. Once a manga ends, it ends. Also, manga moves at a fast paste! By which I mean, there's more action going on in the story than talking about clues and stuff like that. That's why I like manga a little bit better than DC or Marvel.
If DC or Marvel just made Batman or Spider-Man with out any alternate universe or side stories, I would gladly but the comics. I could go on and on, but I would just bore you to death though...