I've found subjects and themes in both Manga and U.S. Comics that I like (I don't like the term comic-book since it puts me in mind of those thin little books. I buy graphic novels to get the full story dammit!) Anyway, there are enough Manga and enough American/Western Graphic Novels to find something great no matter what you're into.
To answer the question directly though (or rather, slightly more directly) I started with manga but am starting to lean more towards U.S. Graphic Novels. When it comes to Manga, I absolutely love the following 3:
Fist of the North Star
Petshop of Horrors
Detroit Metal City
As for U.S. Graphic Novels, there are a lot that I've enjoyed like Hush and, the complete JTHM (just to not name another Batman). At the moment I'm eyeing some of the DC graphic Novels from around the time Hal Jordan went insane and as for Marvel, I'm probably going to be picking up some of the gorier Punisher GNs.
To answer the question directly though (or rather, slightly more directly) I started with manga but am starting to lean more towards U.S. Graphic Novels. When it comes to Manga, I absolutely love the following 3:
Fist of the North Star
Petshop of Horrors
Detroit Metal City
As for U.S. Graphic Novels, there are a lot that I've enjoyed like Hush and, the complete JTHM (just to not name another Batman). At the moment I'm eyeing some of the DC graphic Novels from around the time Hal Jordan went insane and as for Marvel, I'm probably going to be picking up some of the gorier Punisher GNs.