Nicest shotgun? What a difficult question, and I've struggled with how to respond.
The most effortlessly fluid and ergonomic shotgun I've ever lived with has to be an Ithaca Model 37 in 16 gauge. Carried on several continents and over 8,000 museum specimens later, it was an extension of my body in a way no other gun has managed to be. That is good design and flawless engineering, but it is not an expensive gun. I stupidly sold it.
The finest 'factory' gun I have is a Browning Superposed in 12 gauge, pre-Browning production by Fabrique National, dating from the first two weeks of production in 1930, with double triggers. It is perfection in (overcomplicated) design, engineering, and execution. It was made long before corners were considered to be cut, with production milling but hand finishing.
The cleverest I have by far is a Browning Double Automatic, designed by John Browning's son, Val. A rethink of the semi-auto that stands on its own in engineering brilliance, though fallen to obscurity for being in a gun no one ever found a use for.
My collection tastes are in hand-made vintage and antique doubles. At the level of '
best gun,' there really is no difference between a Boss & co., a Purdey, Holland, Woodward or any other of the top makers. Perfection is perfection, in terms of materials and craftsmanship, so none really stand out, for the most part.
The nicest of these that I hunt with is a 12-gauge slide-and-drop hammer double signed Charles William Lancaster of London, the epitome of '
London best,' made in 1864. It was made for the very first central-fire cartridges, and still works just fine.
The finest of the pin-fires I have is a difficult choice, for the reasons described above. At a certain level of perfection, they are all pretty equal. But if I have to pick, a 12-bore bar-in-wood gun by John Rigby & Co. of Dublin, with a Joseph Needham patent action, made around 1868 or so, would be my choice. A hinge-action gun, with the hinge hidden behind wood. Everything about it, from the design to its execution, is as near perfect a hand-made gun can be.