Depends on the day of the month, time, high tide vs. low, and the precise alignment of the planets to be perfectly honest with you. :wink::lol:
There are several threads that discuss this. Really comes down to personal preference. Personally, I started out doing all of mine cap up. Then saw better results with bark, color when I went to cap down. Then I built a drum and cap down was better suited since the heat source is right under the meat. I've never seen a distinct difference in tenderness or juiciness, but now I just go with cap down and it works for me.