Note that it isn't clear that one or the other version is "better" overall. Consider the following abstract:
Converging evidence suggests that the short allele of the serotonin transporter gene polymorphism increases risk for a variety of psychological disorders, including depression, anxiety, and alcoholism. Thus, the short allele is typically considered the “risk” allele, and findings related to the long allele are rarely discussed.
However, upon closer examination, findings associated with the long allele of the serotonin transporter gene share striking similarities with findings from studies of psychopathy. Here, the parallels between findings associated with the long/long genotype and findings associated with psychopathic traits in the areas of neuropsychology, psychophysiology, hormones, and brain imaging are reviewed. It is suggested that the long/long genotype may be a potential risk factor for the development of psychopathic traits.
Andrea L. Glenn , "The other allele: Exploring the long allele of the serotonin transporter gene as a potential risk factor for psychopathy: A review of the parallels in findings," Neuroscience & Biobehavioral Reviews Volume 35, Issue 3, January 2011, Pages 612-620 doi:10.1016/j.neubiorev.2010.07.005