My stepdaughter is getting married in July 2010 and we were discussing flowers this morning. Her inclination is to choose flowers by color and not the type.
I think color is most important. As a bride, we spend so much time coordinating our colors that the flowers have to match or at least fit in snugly, and since flowers as a whole are beautiful, the flower type may not be as important as once thought.
I do believe flower type is a very close second, however!