Wlad - powerful, accurate, frequent output and used for both defence and offence. Oh and also was used to dominate David Toe Haye, who i don't like very much, which is a bonus.
Glad to see Robinson mentioned early. I, however, think heavyweights get overrated in this category because the effect of jabs is more pronounced at that weight. It's easier to tag guys who lack head movement, conditioning, skill, etc. Willie Pep is another who deserves a shout.
I'm probably going to sound like a broken record here, but Thomas Hearns had one of the most versatile Jabs to ever grace the fight game. Be it sticking and moving, blinding to make way for his right, or just plain doing damage, he was able to use that jab for just about anything.
Golovkins jab tenderize folks. Kov is a precursre to the straight right. Fantastic jabs. Loved Holmes's jab as well.