I let my girls pick their own dresses. My only requirement was green (I gave them a few shades as a guideline). I loved that they all had the dresses they loved, and I thought they still complimented each other well. One was very chiffony (middle), one was a sateen cotton, and one had more structure, but still a shiffony overlay. I had earrings and necklaces made, and asked them to wear at least one of the pieces. My sister wore both (in the middle), my MOH wore the earrings and my craft bridesmaid (who made them all!) wore the necklace.
I loved it, exactly what I wanted. I really don't like matchy matchy.