Teófilo Stevenson was as good as any heavyweight in his prime, perhaps even better trhan Ali. He never fought as a pro but he fought and beat the world's best as an amature. Pound for pound I would pick Sam Langford (The Boston Tarbaby) because he fought and won high above his weight division. Except for the colour of his skin he would be rated much higher. That being said Marciano was my all time favourite heavyweight.