I like to theorize endlessly about this. Personally I think it depends on the situation - number of players, mood of the table, and some other variables. If you can set up one kind of image and use it to your advantage at least once in a while, good for you.

Online I like to project aggression and looseness, to get paid off on my good hands. In home games I am happy with my image as a rock, because it means my bluffs are almost never called.