This is a terrible debate and you should all feel bad for having it. Now let me join in.

The research on this topic is split into "completely useless" and "mostly useless". In the former category we have studies that, with a straight face, purport to show that women like nice guys by asking women to self-report on their preferences. To illuminate just how silly this is, consider the mirror case of asking men "So, do you like witty charming girls with good personalities, or supermodels with big breasts?" When this was actually done, men rated "physical attractiveness" only their 22nd most important criterion for a mate - number one was "sincerity", and number nineteen was "good manners". And yet there are no websites where you can spend $9.95 per month to stream videos of well-mannered girls asking men to please pass the salad fork, and there are no spinster apartments full of broken-hearted supermodels who just didn't have enough sincerity. So self-reports are right out.

Other-reports may be slightly less silly. Herold and Milhausen, 1999, found that 56% of university women believed that women in general were more likely to date jerks than nice guys. But although women may have less emotional investment in the issue than men, their opinions are still just opinions.

The few studies that earn the coveted accolade of "only mostly useless" are those that try to analyze actual behavior. Bogart and Fisher typify a group of studies that show that good predictors of a man's number of sexual partners include disinhibitedness, high testosterone levels, "hypermasculinity", "sensation seeking", antisocial personality, and extraversion. Meston et al typify a separate group of studies on sex and the Big Five traits when she says that "agreeableness was the most consistent predictor of behavior...disagreeable men and women were more likely to have had sexual intercourse and with a greater number of partners than agreeable men and women. Nonvirgins of both sexes were more likely to be calculating, stubborn, and arrogant in their interpersonal behavior than virgins. Neuroticism predicted sexual experience in males only; timid, unassertive men were less sexually experienced than emotionally stable men...the above findings were all statistically significant at p<.01"

These studies certainly show that jerkishness is associated with high number of sexual partners, but they're not quite a victory for the "nice guys finish last" camp for a couple of reasons. First, men seem to come off almost as bad as women do. Second, there's no reason to think that any particular "nice" woman will like jerks; many of the findings could be explained by disagreeable men hooking up with disagreeable women, disagreeing with them about things (as they do) and then breaking up and hooking up with other disagreeable women, while the agreeable people form stable pair bonds. Boom - disagreeable people showing more sexual partners than agreeable people.

I find more interesting the literature about intelligence and sexual partners. In high-schoolers, each extra IQ point increases chance of virginity by 2.7% for males and 1.7% by females. 87% of 19-year old US college students have had sex, yet only 65% of MIT graduate students have had sex. There's conflicting research about whether this reflects lower sex drive in these people or less sexual success; it's probably a combination of both. See linked article for more information.

The basic summary of the research seems to be that smart, agreeable people complaining that they have less sex than their stupid, disagreeable counterparts are probably right, and that this phenomenon occurs both in men and women but is a little more common in men.

Moving from research to my own observations, I do think there are a lot of really kind, decent, shy, nerdy men who can't find anyone who will love them because they radiate submissiveness and non-assertiveness, and women don't find this attractive. Most women do find dominant, high-testosterone people attractive, and dominance and testosterone are risk factors for jerkishness, but not at all the same thing and women can't be blamed for liking people with these admittedly attractive characteristics.

There are also a lot of really kind, decent, shy, nerdy women who can't find anyone who will love them because they're not very pretty. Men can't be blamed for liking people they find attractive either, but this is also sad.

But although these two situations are both sad, at the risk of being preachy I will say one thing. When a girl is charming and kind but not so conventionally attractive, and men avoid her, and this makes her sad...well, imagine telling her that only ugly people would think that, and since she's ugly she doesn't deserve a man, and she probably just wants to use him for his money anyway because of course ugly women can't genuinely want love in the same way anyone else would (...that would be unfair!) This would be somewhere between bullying and full on emotional abuse, the sort of thing that would earn you a special place in Hell.

Whereas when men make the same complaint, that they are nice and compassionate but not so good at projecting dominance, there is a very large contingent of people, getting quite a lot of respect and validation from the parts of society that should know better, who immediately leap out to do their best to make them feel miserable - to tell that they don't deserve a relationship, that they're probably creeps who are only in it for the sex and that if they were a real man they'd stop whining about being "entitled to sex".

EDIT: But see qualification here