I think the best jab I've ever seen was Ike Quartey, especially in the mid 90s. Wlad's is good, but he doesn't use it as destructively as Bazooka did. Quartey hurt people with his, it wasn't just to set up another punch.
Pernell Whitaker's would be up there as well. He could vary his jab very well, in a way that Wlad can't.