You see, it's hard because skills/things crosses with each other. Like Kevin Love. He may not the best rebounder, he just hustles too much. Sometimes he is not even box out just try to catch the ball. It helps him to increase his numbers, but it also helps to his matchups sometimes.
And like SB. You need to do several things out there. Play D, help D, move, box out...
But imagine such a drill, just shot blocking. Someone/something shooting the ball from different angles... Manute, Dikimbe try to block as much as possible. Manute would win this and thats why I think he is better shot blocker.
But to block the ball you need to be in the right position,and to be in the right position you need to have good defensive position.
However,it's matter of personal tastes,both were awesome shotblockers :D