They look great!
I was lucky enough to get a few seeds from this pine bonsai nursery in Takamatsu when I was in Japan in 2018. He said they where collected from this special tree with the best characteristics for bonsai, so that sounded promising. They are now the same age as yours!
Anyway, I was having this bud selection dilemma as well because I have a few older pines from seed which I did bud select (also read it on Schraders blog, which is very informative by the way) but it didn’t really pay off for me.
All I got was this very long leader with a long neck and the side branch was long as well, so not very useful as a side branch. I did got this occasional smaller side branch (when selecting the smallest bud from the whorl), but then the leader would still be too long to be used as part of the trunk.
Example of one of my 3 year olds. Not visible on the photo, but there is a tiny side branch at the base of the long neck.
Repotting and root pruning didn’t make much of a difference. I did use this high in nitrogen fertilizer which could have been the cause of the strong elongation.
So what Jonas stated above about thickening or more elongation makes a lot of sense to me now . I think thickening is more important so I’ll just leave the buds on my 1 year olds from now on.
Just one question Jonas: when would you cut the unwanted branches off to avoid swelling if you want that section to be part of the trunk?