I am 19 years old I am not sure which reserve/guard branch is best? Navy, Air Force, Army?

Be advised becoming an officer in the Air Force will be far more competitive since it’s a smaller component. Talk with an officer strength manager before choosing a branch to find out details such as what MOS, upward mobility, etc.

The one that is closest to you. You'll have to drive there every month, if you pick something hours away, it will get old real fast when you have to wake up at 3 am on a Saturday to get there in time

Ultimately it will be up to you what path you take and why you take it. The best thing to do is look at your goals and ask the question with that in mind. For example ask a quesiton like this... I enjoy leading people and accomplishing tasks that involve x/y/z what service and career would folks recommend that would allow my talents to best be used by the mission? I am biased by my past expereince so I will say go AF becuase it give you a chance to do many amazing things but only a few careers will allow leading ground elements so if that is what interests you then the Army or Marine Corps is the best path. If the Maritime environment is of interest and you want to command a vessel and the personnel on a Navy platform then that is a good path for you. Back to by preference to the AF, the cool thing about the AF is it is relatuvely small and the competition is high because you are surrounded by very smart people in general and to succeed you must perform.