I think both for looks and handling concerns, a flat rack and the two side cases is the way to go. To me, a top box only looks top heavy and scooter-ish (not that there's anything wrong with scooters). The side cases are easily removed if you want to go naked. I haven't factored cost into that recommendation, but it's what I would pursue. I guess it also depends what you want to carry and what luggage would best accommodate it.