Best branch of military to join to be a Civilian police officer.?

i am 17 and i want to be a police officer. i am thinking about joining the military for 4 years to get some expierence first. i want to do something in LE in the military. i want to patrol and make bust, not just stand around and guard stuff. i have done research on Navy MA and Air force security forces which i heard is a sucky job. would like to no info about coast gurard LE i heard that is the best route to go. i am planing to join this year at the age of 17.