difficult to say, I guess it depends on which fish they are in with. For example, a tomato clown would be ruthless towards another clown, especially if they are different species, but towards an angel, I think he would leave it alone and may just chase it out of his territory. As for the angel, towards other angels, he too would be aggressive, but towards a clown, i doubt very much would happen.
So to answer you question, between the two, they both can be aggressive but most likely only to their own kind.