In response to that one debate you had in 8th grade health class that ended abruptly because there wasn't nearly enough coffee or cigarettes in the teacher's lounge to put up with that crap, and really, Jesus Christ, ASAP Science has attempted to answer who has it worse: women in child birth, or men who have been kicked in the junk.
OK, so this one is hard, because there isn't an actual measurable unit of "pain", despite internet folklore on the subject. Pain is actually received by sensory neurons called nociceptors, which send nerve signals to the spine or brain. They can fire off either dull, achey pain, or sharp, OH GOD HELP (response-inducing) pain. For the testicles, which are rotten with the things due to their importance, that sharp pain is compounded by the fact that the nociceptors are connected to the stomach and the brain's vomit center. So, that hurts.
For women, it isn't really any better. The uterus is also lined with loads of pain-firing nociceptors, and they're under duress for hours at a time during labor. And then there's the nausea, fatigue, and "stretching" (and tearing and involuntary pooping, and...).
Since pain is subjective, and not really measurable, the debate is called a tie. Pain is different for different people. Though, a humble dissenting opinion might look something like: SHUT UP FOREVER SHUT UP OBVIOUSLY CHILD BIRTH IS WORSE SHUT UP. At least until the next time you see a highlight of an umpire taking a fastball to the crotch. [YouTube]