If your "best" shot means a good shot you made that you'll never forget, then mine was also with a BB gun. I was about 7 in north GA and spotted a small bluish bird roughly 30 to 40 yds away in the top of a pine tree. I wanted to miss it and just scare it, but, as so often happens, the miss turned into a dead on hit. It fell to ground like a rock. The bird turned out to be an Indigo Bunting, the state bird of GA at the time and shooting it was a misdemeanor. Fortunately, no one from the GBI was around at the time, but my mother wasn't pleased to say the least. That one shot made me determined to shoot better so that when I wanted to miss, I would.