I think the thoughts or feelings you want to express dictate the style of music you write in. To some degree, at least. One-trick ponies don't make it. I think if Britney Spears put out a song to raise awareness of the AIDS epidemic in Africa, for instance, the message would get lost in the production.

I happen to like Blues for its ability to express a wide range of emotions. I admit my own efforts are too deeply jazz-tinged to claim any sort of purity, but I can get my meaning across. If I felt like I'd had way too much Sht'n'abuse, my writing would come out with a lot of screaming metal in it. My most abstract mood pieces get written on an acoustic 12-string.