A lot depends on whether the house is new or already occupied. If new, spray painting is a much faster way to get the paint on the wall, especially if the trim isn't in place yet. Everything that you have to move, mask, or cover (furniture, trim, doors, windows, carpet) will slow the process down. You'll get a lot of "bounce-off" with an airless sprayer, that usually falls to the floor. You will need to cover anything that you don't want paint to fall on. Rolling, while usually slower, does not require as much covering and masking. You can also have several people in the house rolling at the same time, which cuts your total job time.