I'll give my 2 cents since I've owned both Jesse Bags and Happy Trails. I prefer...wait...Jesse Bags. Both are top loaders which I prefer but the Jesse bags and rack are bomb-proof...as I've gone down off-road on both. The weak point of the Happy Trails bags are the rack as they suffered some good damage. I don't think I'm prone to dumping my bike. I just take my 800GS where it was intended and shit happens. I also prefer the hinged top on the Jesse Bags plus they can be more easily taken off the bike and used for a make-shift table if you like to rough-camp in the middle of nowhere. I probably should own some plastic boxes as I like to push it since they seem to withstand a fall better...but I don't like side loaders as my stuff will fall all over the place.
Johnny da Rock