A lot of people have commented on how high I wear my guitar strap, but I just set it to the height where I can play everything easily.
When I was younger I wore my strap low because I thought it looked cool, but over time as I evolved as a guitarist I began raising my strap.
These days I set my strap so that my guitar is in the same place as when I play sitting down. I want to be able to reach the hard chords and play melodies easy on the lower frets.