"I was wondering what the best designed and best finished of the early American SXSs. Before the Winchester model 21."
Here was the original post. It definitely specified ""American SxS's".
That leaves out O/U's as well as all pumps, semi-autos etc as well as repeating arms be they shotgun or rifle.
I acquired my first Lefever nearly 50 years ago. I still like its design better than most any double I am aware of & this includes many, if not most foreign doubles as well. The gun can be taken apart & put back together with no hang-ups regardless of whether the hammers are cocked or down in the fired position. The firing pins never hang in the dented primer causing difficult opening. You need no special tools to re-install the hammers & mainsprings, nothing to push around like an L C Smith, & certainly to struggle like a Fox, one of the hardest guns I ever tried to put the hammers back in. Incidentally those side plates on a LAC gun are not just "Dummy" plates as on most side plated box locks. They allow access to the locks. The hammers, mainsprings cocking hook & some other parts can all be removed after taking off the plates without removing the stock. The top hung sears offer much better leverage against "Jar Off" than a typical boxlock. Design wise give me a good LAC gun anyday over the Famed A&D boxlock. All these little things add up.
As far as American guns go I am still of the opinion that Parker Bros generally had the best "Finish, especially inside. As said they needed it to work at all, though they did through this better finish end up with a smooth working gun. For equivalent barrels, stock & decoration though they were also the highest priced.