One thing I took away from the interview with the writers was that Brian was their central character, not Michael. Brian was my favorite character, too, for the same reasons cited by the writers.
Though many saw him as the "heavy" he was in fact the most moral among the group of friends. And he always was the guy who came to the rescue of his hapless buddies, usually behind the scenes. He may have been perceived as ruthless & selfish, but in truth he was more generous & thoughtful than all of them combined.
I liked that contradiction, which I though did demonstrate good character development by the writers. Not everyone 1-dimensional, all black or white.