In a small bowl, combine the brown sugar, salt, mustard, garlic powder, black pepper, cayenne and paprika. On 2 baking sheets, sprinkle the spice mix all over the ribs, pressing and patting it into the ribs. Cover with foil and refrigerate for at least 4 hours, overnight if possible.
Preheat the oven to 250 degrees F. Keep the ribs covered in foil and roast for 3 hours, until the meat is super tender but not falling off the bone. Remove from the oven and pour off any liquid on the baking sheets.
Preheat the broiler or BBQ. Brush each rack of ribs liberally with the various barbecue sauce and broil or grill for about 10 minutes, turning and brushing occasionally with the sauce, until well-browned and crispy in spots. Transfer the ribs to a clean cutting board and let rest for 5 minutes. Cut in between the bones and mound the ribs on a platter. Pass any extra barbecue sauce on the side.
Serve alongside extra BBQ sauce for dipping, some pickles and some chips.