Butts are so forgiving, you could do it either way with good results, I put mine fat down. The meat itself has about 2 cups of fat all sealed up inside and will render out during the long cook, thus keeping the meat moist. The spraying of juice, or a mop is just to keep the outter bark from turning to leather. It doesn't do much if anything for the actual meat under the bark.
SFL is right, this question will never be answered. I hope you first timers enjoy your smoke tomorrow, I know its hard to do, especially when your new at it, but try not to do too much peeking, or showing off the butts to others. It really prolongs the cook time. When you do hafta open to check/ rotate, spray....ect. do it as quickly as you can and get it shut back up. Be patient, keep your temps as steady as you can with your equipment. You will know when the meat is done by temp, and feel.
If you are takin the butts to 195-205 for pullin, you may need a big strong wide spatula to get them off the pit without falling apart, unless its in foil. The thermometer will slide right into the meat like warm jello, and the bone should pull right out easy with just a lil tug, if you grab it to pull the bone out and it wants to stay in the butt, its probably not done as well as it could be. Have fun, and enjoy. Don't eat too much, leftovers are wonderful!