Personally I change my exercises pretty much from workout to workout, however I stay in the same bracket. For example, I train using a total body 3 times a week. I always do some sort of upper body pushing exercise. Could be Bench, Incline Bench, Close Grip Bench, Military Press, Push Press or any of the above with dumbells. Train the movements, not the exercies. Unless of course you are a powerlifter I guess.