What about all the laughing so hard you're crying? Or being so upset you're cry-laughing. How do we factor those?
Also I'm going to say laughing. Alot (most people) laugh multiple times a day, i know i do. I very rarely cry, in fact it's been years since i last cried.
So yeah, its clearly laughing.
EDIT- shit, i didnt think about babies. Stupid babies ruining it for everyone else!
People laugh a lot, even in the most terrible places. I don't often hear people cry loudly other than in funerals, and even then it's only for a few moments. People try to celebrate the dead's life if possible. And for every newborn crying, at least one person (parent) would be laughing, right?
I'm almost certain it's laughter. When I cry or see someone else cry, they don't really make noise. The only people who I think actually bawl are drama queens and children. Also people laugh way more often then they cry, I laugh hundreds of times in between crys. The baby thing is a decent argument, but babies account for a tiny tiny fraction of the worlds population.
The stipulation of 'sincere' laughter should also be imposed on crying. Since I'd argue that babies crying is a completely different thing from an adult crying as it's unrelated to sadness and more of an instinctual method of communication. Whereas laughter is always a result of happiness, even in babies.
So if you accept that, laughter would definitely be louder.