Do you guys prefer building for looks or for function? For example, do you have empty rooms or buildings that serve no immediate purpose, or do you have structures that are utilized to their full potential?
For larger projects(Like a restone minecart station for instance), I try to make everything as functional as possible first, then worry about aesthetics later. I'm majorly paranoid that I'll have to break a whole wall of glass just because I forgot something little.
Always form. There are only a few basic functions of a building in Minecraft, and I have never had a problem building something for form that fulfills those functions. Some functions add form (like spider-proff castle walls that have flaming patches for both killing and light.