Both methods are good ways to store a two-person sleeping bag between camping trips. The important thing is to keep the bag open or loosely packed so that the inner insulation can recover and maintain its loft. That loft is what keeps you comfortable and warm, but only if it’s dry and air is able to get between the insulating fibers. Make sure the sleeping bag is clean and completely dry before storing it. If you aren’t able to hang it up to dry, stretch it out in an unobtrusive place for a couple of days before rolling it loosely into a breathable storage sack.