Assuming none are taken, then the right one against the wall. That way if someone else comes in and they are short, they have the one that is for them. If they are normal size, then they can use the toilet since one never should get right up next to a dude when pissing unless there are no other options.
Definitely not the middle one because then you are both exposed and you then automatically made it a harder choice for the next person that came in - they pretty much have to go to the toilet, whereas if you are to the far right they have a choice.
Also, there is always the sink or one's own pants.