I have Price, Hamels, Bumgarner (all 200K Cy Young type guys who have a shot at winning 16-20). Then I have Lohse, Buerle, and Jason Vargas and I just picked up Shelby Miller and dropped the Japanese guy from Seattle. That is a very, very solid rotation and I also have 4 good closers.
You want to have options at pitching so you can play matchups or start 5 guys on any given day or sit them if your opponent has nobody starting and you're winning the SP matchups. Then your RPs take over.
You want your everyday lineup to almost never change...that's why you should load up on guys that get over 500AB and produce numbers.