I'll read anything good, but manga on the whole seems better to me. It's a far bigger industry and thus has far more variety. There are some wonderful American series, but not very many of them... and the good series like Spider-man and X-men are caught in a loop of rehashing the same story over and over again in different 'incarnations'. The only American series that has really stood up and been consistantly wonderful in art, story, and everything else is Sandman and its related stories.

With manga, there is of course a lot of crap. But I've found a large chunk of wonderful series, especially stuff that doesnt run on long after it should have stopped (though there are series, especially by Rumiko Takahashi, that do so). I dont think I've ever encountered a manga series that does a 'retelling' of its principle story once it's run into dead ends in the normal storyline.

I've got a very long list of favorite manga, and only a short list of favorite comics (graphic novels, folks, are collections of comics OR manga. They're just comic issues bound togther, manga is usually initially published in magazines and the like, then bound into the graphic novels we see in America).