The antenna closer to you / easy to access should be the Master
the reason being is in case you need to change the frequency of the Master / AP antenna and after the change, if the other site does not pair then you need to travel further to physically access the Master antenna and play with the frequency parameter. And if the Master is mounted high on the pole then good luck getting a boom truck.
But if your Master is closer to you or the Master is at a location that is easy to access then you don’t have to climb the pole to physically access it.