It depends not only on personal preferance but emotions you what the fans to get from what your music. I like to break things so i prefer fast or moderatly medium stuff. You could screw up either and end up with crap, fast is harder to mess up because its fast but if done good it destroys all compation. A perfect example is Cliff Burton, his stuff is fast and it supports and expands the whole rest of the music.
so i prefer fast or moderatly medium stuff. You could screw up either and end up with crap, fast is harder to mess up because its fast but if done good it destroys all compation. A perfect example is Cliff Burton, his stuff is fast and it supports and expands the whole rest of the music. 
