Hulk withstanding the Browning M2:
Superman withstanding the Browning M2:
The BVS DVD commentary said, that to Superman, the bullets felt like being "hit by base-balls at 60 mph", which suggests that they were hurting him (which is likely considering he is being pushed by, whereas the Hulk was not). Hulk actually withstood the Browning M2 without actually having to defend himself. It seems that his damage soak (at least in this scenario) is greater than Superman's.