Based on a meta-analysis of the correlates of physical attractiveness (Langlois et al., 2000), it is probably accurate to state that physically attractive people do have slightly "better" personalities, at least in some ways. The effect size links between attractiveness and personality in terms of the d statistic are:
Extraversion d = +0.26 (based on results from 9 studies)
Intelligence d = +0.07 (based on results from 18 studies)
Mental Health d = +0.16 (based on results from 19 studies)
Physical Health d = +0.38 (based on results from 5 studies)
Social Skills d = +0.20 (based on results from 18 studies)
These effects are small in size (hence any one study with a small sample size may not find the effect is statistically significant), but the effects are not negligible from a meta-analytic perspective.
In a more recent study using a nationally-representive sample of the USA, Nedelec and Beaver (2014) found robust links between people's physical attractiveness as rated by others and their mental and physical health. For example, more attractive people were less likely to be diagnosed with several chronic diseases and neuropsychological disorders. The researchers concluded that physical attractiveness is a reliable sign of health.
Although the specific cues that people attend to when they judge physical attractiveness can vary across cultures and historical time, an evolutionary psychology perspective suggests some cues likely transcend time and place.
For example, evolutionary psychologists have hypothesized that women possess specially-designed long-term mate preferences for cues to a man’s ability and willingness to devote resources to her and their offspring. Such cues may include a man’s status and prestige which, depending on culture, may involve hunting ability, physical strength, or other locally-relevant attributes, as well as his ambition and work ethic, intelligence and social dominance, and slightly older age.
Human males, on the other hand, are thought to have evolved preferences for cues to youth, health, and genetic quality as these provide useful signals of a woman’s fertility status (i.e., odds of conceiving currently) and potential reproductive value (i.e., the number of children a woman could have into the future). Thus, men are expected from an evolutionary perspective to desire physical features indicative of a woman’s relatively youthful age (e.g., neotonous face, full lips, clear and glowing skin, clear and wide eyes, small chin, lustrous and long hair, good muscle tone), to desire physical features indicative of high-fertility estrogen levels (e.g., high femininity in face, voice, finger lengths, and a .7 waist-to-hip ratio of body fat distribution), and to desire physical features indicative low genetic mutation load (e.g., facial and bodily symmetry).
When men and women pursue short-term mates, different cues can become more important (e.g., women focus more on cues to genetic quality). Several lines of evidence have been used to evaluate the existence of men’s and women’s long-term and short-term mate preference adaptations, including self-reported mate preference surveys, reactions to experimental manipulations, cultural artifacts and historical records, ethnographic evidence from pre-industrial cultures, examinations of actual mate choice and its marital consequences, and evidence from actual courtship effectiveness and associated fertility outcomes. Generally, results have been supportive of evolutionary perspectives.
Langlois, J. H., Kalakanis, L., Rubenstein, A. J., Larson, A., Hallam, M., & Smoot, M. (2000). Maxims or myths of beauty? A meta-analytic and theoretical review. Psychological bulletin, 126(3), 390-423.
Nedelec, J. L., & Beaver, K. M. (2014). Physical attractiveness as a phenotypic marker of health: an assessment using a nationally representative sample of American adults. Evolution and Human Behavior.