I give oscar credit for the hook. He gets opponents leaning and they pay for it. At lighter weights he was something else.. Quick, crisp, and powerful left hook, but unfair advantage being naturally left handed.
If you're going to put Robinson on there - then there is simply no competition. Aslo - Oscar De La Hoya deserves a place on this list as well. Ask Vargas, Quartey and Mayorga about his left hook.
That snapshot is from a clip of Merchant shoving a fan that interrupts his post-fight interview. You can find it on Youtube.