I think it’s funny how John is the response to what Hans best friends name is considering John was a very popular name throughout history.
But based on the Frozenverse I think the quote would be more likely to be “probably Lars” (for analytical prevalence).
Just off the top of my head there is (1) Lars who’s Hans brother, (2) Oakens cousin, (3) the baby reindeer, (4) Oakens pet mouse, (5) as well as various other characters from an ice harvester to a couple children and a quickly mentioned townfolk. There are probably more too but I haven’t read every Frozen book yet unfortunately..
I cannot think of very many Johns……I can’t think of any John at the moment now that I think of it. There probably are some though.
Oh, we could also include Miss Larsen’s relative of some point in time to be another Lars character.
There are other common names throughout the ‘verse like Bjorn, Helga, etc But I believe Lars is most used by far.