A set of RocketIII OEM bags are stout and very handy with the quick release fasteners. As a daily user of my bag capacities, whether that be toting lunch or picking up a few loaves of bread and tonights supper, I've found them to be the shiznitz. A full fork width tool bag and a rainsuit reside in the bags as well. The downside of the very tough leather bags is retaining their like new shape for more than 12 months, without the Flipmeisters bag stiffeners.
IMO, if you're going to have bags attached 24/7 then leather is the best choice. Leather will stand up to the elements far longer with minimal attention and still retain the best appearance. Cracks, crevices and fabric weave are a detriment.