Though the best course of treatment for an anxiety disorder remains trial and error for now, doctors and patients aren't entirely in the dark. Some predictors point to whether therapy, medication or both will likely work best for a patient.
As a general rule, the milder the anxiety is, the better patients tend to respond to psychotherapy.
People who are more insightful and committed tend to respond better to therapy... They must be able to determine why they feel a certain way and to talk about it, and since treatment is very interactive and can be tedious, they have to be motivated to do the work.
Access, of course, is another factor in the probable treatment course: A lot of people see a primary care provider, get medication and never see a therapist. Medication is a lot cheaper than therapy, which is not always covered by insurance.