Prime Roy ducks Prime Hagler. The Hagler that fought SRL was ****ing old and slow. He loses to Jobes easily. But not Prime Hagler.
Truthfully, a prime Hagler would put a lot of pressure on Roy Jones and see if he would break. If Roy fought with Hagler he would have been kayoed, so he try to box, which may have been successful for a while, but I think Marvin's long reach and great timing would have eventually enabled Marvins to land enough shots to tko Jones late in the fight.