How well did you know them both personally? To compare,,that is.
I met only Miłosz. I don't have to know them personal to compare. Also Miłosz spent most of his live in America. Should get his prize as an American. He even wrote some of his poems in English, that telling.
Their poetry is distinctive. I don't really think, that you can compare poets or any other writer, painter etc. and measure which is better. You can only say which you like better.
I think that you can say who is a better poet.