A hard box is best on weather, security, noise and aerodynamics. It is the most expensive, it needs crossbars, and it lives on a garage wall for eleven months of the year.
Where the vehicle decides the box we rank by vehicle: cargo boxes for a Subaru Outback works the published roof limit for each generation against what an empty box weighs, which is the arithmetic that decides the size.
A soft bag is cheapest, folds into a closet, and some work on a bare roof with door-hook straps. Worse on everything else, and the right answer for one trip a year.
An open basket takes shapes a box refuses and costs less, at the price of no weather protection and considerably more noise. A basket plus a waterproof bag plus a net is the value combination people overlook.
We compare all three properly in roof rack vs cargo box. For the two category winners in detail, read the Thule Motion 3 review — including the three cases where the cheaper Force 3 is the better buy — and the Yakima LoadWarrior review for the honest limits of an open basket.