Pelican cases (Caribou) are the softest of the hard bags. Since they're thick, tough plastic, they have the advantage of not denting. Once they get scraped up, they still look fine. In fact, I consider them sufficient low-speed drop protection that, in conjunction with the Yamaha plastic crash guards, I don't need to bother with other crash bars.
Moveover, they're lockable, quick to mount/unmount, waterproof. One ends up with a 24x40" flat space on top of the bike which can be used for a huge dry bag or fully loaded backpack. Since they're side-opening, the contents can be accessed at any time. The liners prevent the contents from spilling out, so they're similar to top-loading, but much better. Helmet won't fit, so I lock it to the grab rail with a small cable lock I carry in the side case.