Round, and no more than 2 of the same pattern! Oh wait, that's not right, we DO have 4 of the Disney plates they had at Mickey D's (I think) several years ago, and 4 matching square Mickey tropical plates that we never use. None of them are glass, either. Even though we no longer have small children, my DH and DS seem to have enough trouble not breaking my glass mugs, etc!
We also use paper plates a lot!!