Im new to bonsai...this mugo has made the july cut(been trying to do bonsai for about 2 years now. an outdoor plant making it through JUL is a 1st for me...)Since this seems to be a tough bugger I want to make sure I do it justice.
Thanks for the pix fix, Will. It seems that there are three possible upper trunks. I think a lot of people will suggestion using on of the side stems as the main trunk, but my vote is to use the middle one. This will create some nice taper and be a little subtle than the using one of the side trunks.
In this very rough virt I took the first picture above and rotated the tree 120 degrees counter clockwise. I also drew in a quick pot, nothing else was done. Looking at the rotated tree, I see another interesting possibility.
I don't think there is any need to go to that extreme with this nice little mugho. It's hard to tell with only these views, but my suggestion would be to use the "middle" trunk like you said, and keep the lowest one for the first branch for now.
I think you are on the right track with the upright styling of the tree. In my experience, one of the three trunks will need to go to avoid a swelling in the trunk where they meet.
A better picture would help, thanks Will for brightening them up, but the only real way to determine what to do next has to be done in person. If you feel strongly about the styling, then that is probably the best option for the tree.
Make sure it is healthy and strong before you do too much work on it. Try to get a local opinion on what to do and when. You are off to a good start on this tree, keep it up!