I have to say my knowledge of Monzon is minmimal as he seems to be a forgotten man in boxing with never a mention of him but he was tall and rangy and held the title with a far tighter grip than Robinson.

In the words of Monzon himself, 'Robinson may have won the title 5 times, but he lost it 4 times, I won it once and never lost it',

I go

1: Monzon
2: Hagler
3: Robinson
4: Hopkins

The likes of Greb, Zale, Ketchel, Bassilio etc I havn't seen enough of to comment.