So to solve the problem, they let the dog decide. Both people stand far apart with the dog between them. Then they both call the dog at the same time. Whichever person the dog goes to, gets to keep him.
The way I decide between two formats or sizes is: I fill out my entire week in both formats/ sizes with my appointments, tasks, special events and everything else for the whole week. For example, if I am having a really busy time, I fill out the week in my A5, and also in my Personal size to see if I can figure out techniques to make my Personal work well enough when I am very busy, or if I have to have the larger page size of the A5 to write everything in. During the course of the week, I pay attention to which one I look at and use more. The one that works better for me at the time is the one I either switch to or stay with. Usually the winner is apparent after just a few days.
I’ve just now realized that it’s my planners calling me, and whichever one I go to gets to “keep” me. Which means I’M the dog!! Maybe I should come up with a different name for this!