I wont to join the marines but im not sure about what field is the best to go i got 3 choices?

i wont to join the marines but im not sure about what field is the best to go i got 3 choices and the are a speciall ops/combat unit or military police or i thought about doing amechanicc thing but im not sure but i know after the military i wont to do lawenforcementt or be and athletic directer wha would be the best field to choose from and how long i should stay in there so can some one mabey a recruiter or some one explain what would prob be the best option