Lot's of heavyweights here -- probably because the jab is more influential there. I'm going to have to stick up for Winky Wright. He himself is not nearly as great as most boxers mentioned in this topic, but he's beaten great fighters with little but a great earmuff defense and that demon jab.
In his second fight with Rocky Juarez, Barrera throw perfect jabs all night. I don't think I can remember such an effective display of jabbing to a victory at a low weight for a LONG time.
I think Hearns and Holmes had the best jabs ever. Hearns has to be in the category of best jab ever. He outjabbed Virgil Hill who had a great jab.