Karn

My ranking would be like this:
1. Novel
2. Manga
3. Movie

*slight spoilers on the differences between the three versions*

I read the novel first, but I could be biased in that I had pre-conceived notions as to how I thought the manga and movie should play out. I liked it the best because:
A. Fairly detailed background info on many of the characters, including those that didn't get much info in even the manga, as well as a look at how these characters play out the "game" and what is going through their minds. And stuff.
B. Though there are a lot of violent scenes, it isn't as gratutious as the manga (though, to be fair, manga is a "laid out on paper" visual medium and the whole premise of the BR story is violent in general)

As for the manga, the thing I like most about it is it features my favorite character, Sugimura, quite a bit (the novel does this too, but the manga changes things completely by the end - and his backstory is much more developed). And while I am not a fan of the over the top violence the manga went for, it does seem apt. However, the additional Mitsuko stuff was too "shock value"ish for me.

Another minor gripe I have is with Keith Giffen's Tokyopop adaptation. While I'm a big fan of Giffen's Justice League, short lived Suicide Squad, and so on, I thought some of the slang used in the BR manga was kind of strange. Perhaps I'm just not with the times, though.

And finally, the movie. I saw it and liked it. Very stylish, but there was something missing, and I guess the message of the movie was supposed to be different too. What that is, I have no idea, perhaps the Old vs. young thing. "Beat" Takeshi's performance was awesome though.