How about a good old-fashioned who is the best horse argument?
Not is one of them the best horse ever, because few of us have seen the Sea Birds etc.
The question is Who is the better horse of the two? Most have us have seen both of them so can make an informed opinion.
For me, Sea The Stars. He won at 8f, 10f, 12f; he won two classics; won at home and abroad; and many of the horses he beat won good races when he wasn’t around. And he had a perfect temperament.