I dont really know about know.. 4 years ago it was Kessler by far, he may had the best jab in boxing back then.. But i still think it is Kessler..
4 years ago it was Kessler & Wlad Klitschko sharing that top spot. What the OP really meant to ask was : Which Super MW brotha has the best jab ?
Bute outjabbed Johnson even though he had the shorter reach and that was the case in many of his fights.