Not sure about the best but Qawi had a really good, active jab for someone so short...by the division's standards.
Montell Griffin did very well at range for a very short guy. His performance in the first Jones fight shows him often befuddling and out jabbing a taller,faster opponent at range.
liston had a great outside game,and he was a big man for his time,but today he would be short for a hw
Canto's outside ability was top banana to say that he was only 5'1. Wee Walter McGowan was only about 5'2, and he was a splendid little pure boxer despite often being at a disadvantage in both height and reach. He was outfoxing the bigger Chionoi both times before cuts bollocksed him up, held his own with Rudkin who was classy at long range and even had the odd success up at feather (albeit against more limited opposition).
Yeah i've seen some McGowan, good call. Rudkin as well, he was more of a technician but he was quality at range.