What field of psychology do I want to study?

Firstly, should you wish to pursue a career in which the clinical environment of therapy and the scientific edge of research are integrated, I would recommend you invest in a joint M.D./Ph.D. degree. By equipping yourself with this confluent academic merit, you can partake in both psychology as well as the research whereby science is translated into clinical practice. Proceeding to the sub-genres of psychology, or in the context of medicine, psychiatry, there are a variety of options that cater to the individual interests of the aspiring professional. Clinical psychology typically pertains to aiding individuals with their personal dilemmas and regimenting cognitive behavioral therapy as an intervention to quell these problems. In addition, psychologists are trained to diagnose mental illnesses, such as depression, as well as functional syndromes, such as autism. Psychiatrists preoccupy themselves with similar activities, however, they exercise the power to prescribe psychoactive medication to treat mental illness, and subsequently have a broader understanding of psychopathology in a neurological context. Psychometrists are the mathematicians of the discipline, quantifying values of intelligence, social competence, and mood via psychometric examinations such as the ever-prevalent IQ test. Moving from the clinical environment to that of the research institution, cognitive neurologists seek to elucidate the neural substrates governing behavior, grounding lofty concepts such as philosophy, perception, language, and personality into the hard-wired biological construct of the brain. Evolutionary psychologists describe the benefits certain behaviors pose for Darwinian individual selection and survival value, explaining why the different sexes act in idiosyncratic manners, and why counterintuitive reactions such as aggression are evolutionarily viable. Behavioral genetics and psychogenomic science attempts to pin down phenotypic behaviors and brain structure to an isolated gene or larger hereditary unit. Finally, neuropharmacology serves as the pharmacy for the discipline, producing novel psychiatric drugs in response to the clinical needs of those who suffer from mental and cognitive illnesses. Note that these categories are rather broad, and can be further dissected into even more specific fields that pertain to esoteric studies, such as biomusicology or sexology. Given this candy shop of choice, it is of my personal observation that cognitive neurology is certainly the most vogue field in psychology during the modern era. Society is beginning to acknowledge the irrefutable role biology plays in determining behavior, and as such, research has accelerated in response, with many of the most profound discoveries on thought and behavior being made in the last decade or two. Yet, the value of the field transcends mere behavioral theory and scientific titillation; the advancements made in these disciplines represent a hope for many suffering from the gamut of psychiatric illness. It truly is science with a purpose. As such, my own personal verdict would recommend a career in both clinical psychology and cognitive neurology. You get the best of both worlds; the intrigue of science coupled with the seeing the face of who you're doing the science for -- people.