Great thread topic! I would say my top picks, in no particular order, are:
1) Larry Holmes: When his legs were still fresh he was able to dominate and control a fight with that jab. Lump guys up, control the pace/distance...etc. He would use it to set up his right or combos. Strictly my opinion, but I think he beats out the other great jabbers in heavyweight history (Bowe, Lewis, Ali, Wlad, Liston) as far as jabs go. All of those guys mentioned though had GREAT jabs. Side note: in my opinion Tim Witherspoon n Ray Mercer had very underrated jabs, when they used them.
2) Oscar n Ike Quartey. Both had great jabs and could dominate a fight with them. Oscars was a little faster in my opinion, but Ike's was stronger and came from an unorthodox angle. I really enjoyed their fight and thought that each guys biggest issue was the other guys jab.
3) Sweet Pea Whitaker: Great Jab and could control larger fighters with it, keep distance, set up combos, break the other guys rhythm, use it offensively or defensively...etc. Great jab.
4) Virgil Hill: Was a long time and multiple weight titlist with little more than a jab.
5) Floyd, Hop, James Toney. All use the jabs similarly in my opinion, but Floyd's is the fastest n best, especially his effectiveness with it to the body. Hop used it to perfection vs Tito and in my opinion only loses to Floyd because of speed n use to the body (jab). James used his less than the other two, but like everything else he does, is textbook perfect when he does use it. Well, everything except train n stay quiet, not too textbook at those things. I lump them together because all three have dominant jabs and use them effectively but often "blade" their bodies n prefer to slip n counter or lead with the right (Fkoyd n Hop) or left hook (Floyd).