Probably Sugar Ray Robinson. There's a segment in the Bobby Dykes fight where he noticeably throws it way more than the jab to the head. I also love how keen his eyes were for details, and how quick he would adapt to them. This content is protected At 1:20 he instantly notices that Graziano drops the right hand after the body jab. A lesser fighter would have probably set a pattern to get Graziano to open up. But Robinson immediately goes to work by feinting the jab to the body again, and nails Graziano with a right to the head.
IDK about all time ranking, but the one Floyd Mayweather put on Robert Guerrero was about as good and effective one as I've ever seen. And of course DDs against Usyk was championship caliber
Floyd Mayweather and Andre Ward were great at sticking the jab to the body. I believe Sergey Kovalev also knocked out a fighter with one hard jab to the body. Currently Naoya Inoue showed a great stiff jab to the body, as shown in his fight against Stephen Fulton.