Which treatment works the best and fastest for post nasal drip?

Postnasal drip. The standard treatment is with an otc antihistamine like Benadryl (diphenhydramine) (sedating) or Claritin (non-sedating). If this does not control symptoms, the next step is to use the combination form of antihistamines like claritin-d, or allegra-d. If that doesn't work, you'll need to see a doctor for a prescription medication.