The easiest choice would be the Guest Relations windows just outside of International Gateway. I usually don’t go to a park on check in day, so I have gone there in the afternoon many times, and it wasn’t very busy. I imagine it would be busier early in the morning.
I agree with the GR at Epcot IG. You go through security, then turn left and it’s in the building there. We’ve often activated APs or even purchased APs there in the past on checkin day and haven’t found it busy.
I was there about a week ago. I had a new AP that I bought online. I had to go to a ticket window to activate it. I was staying at Bay Lake Tower, went to the MK ticket window after I arrived late afternoon.
We did that in January. It was very convenient. Prior to the reconstruction of the entry plaza bt the IG, there were two separate kiosk buildings, left side was GR and right side was ticket sales. Now, both are located in the building that houses the restrooms and lockers. It looked like the same group of cast members staffed the ticket windows outside the building and the GR desks inside, so I think one could activate in either location.
