Which one is the best to treat obsessive complosive and social phobia. sertraline or paroxetine?

Patients come first: This is not how medicine works. When comparing similar medications one has to take into account the patient in front of them first and their likely reaction or side effects to the medications under consideration. It also depends on the history of other meds they are on or have tried.

Alt.behavioral: While researching meds, consider researching effective behavioral/psychological treatments: to conquer social anxiety the "gold standard" treatment is graded exposure/systematic desensitization. To take charge of ocd, the gold standard is exposure & response prevention. A clinical psychologist specializing in anxiety can be huge help. Learn about at anxierybc.Org. Also see ocfoundation.Org.