I wouldn't pick the Winchester 21 as the most graceful looking shotgun around.
I spent about 30 yrs full time in the restoration biz mainly on sxs shotguns and had just about everything pass through my hands for some kind of work including full restoration.
Maybe I've seen too many different SxS's but the Win21 never struck me as anything special inspite the mfg'rs claims.
They can be made into a nice shotgun but generally how they came from the W factory was nothing outstanding when compared to other mfg'rs offerings.
They did put some nice AmWalnut on them in most instances I will say that.
The older classics like Fox, Parker & Lefever stepped up to Euro Walnut as the grade went up.
Fox can be criticized for down grading it's engraving quality after WW1 to save $$ with those crazy save-time designs by Gough.
Winchester 21 engraving was always crippled by the extreme hardness the frames and forends were heat treated to. An engravers nightmare to cut even when carbide tools came one the scene.
Annealing was not an option for factory engravers but outside workers often did and their work will show fine quality detail the factory cutters never seemed to achieve trying to carve the near impossible to cut HT's steel.
The Win21 is nothing special as far as design,,and neither is the AH Fox or Parker. They all have their quirks and flaws.
They all break and wear out and need repair.
The 21 is the easiest to repair right now because of the availability of parts from CSMCo who continues to mfg the Win 21 under license.
Problems with the ejectors on a Win21?,,buy every part in there if you need to (and can foot the bill). Try that with an elderly Parker or Fox and it's hunt for parts time. Though orig Fox parts are in pretty good supply now from a source in the NY Adirondaks. Many are in rough out form so be ready to file,,then file and fit some more to end up with a part. But it's a good source.
I recently made up an ejector forend complete to fit an existing AH Fox 16ga SPE that was a 2 bbl set and the second bbl was located. The extra ejector forend iron and forend were made up of rough orig Fox parts to fit the old newly located second bbl.
My pick for the 'nicest looking' SxS's would be the pre WW1 German &Austrian made guns.
They are everything as far as quality that the Brit guns are in the mid and high grade guns and the styling is what I would call exactly what I would want.
That comes after just completely restoring a 1896 Purdy 16ga self opener SxS 2 bbl set.
Killer wood under all that grunge,,but I still favor the German products of the era.
But like Mike, SC Hunter says,,,Beauty is in the eye of the beholder....
....I go to the Skeet range and shoot a 1925 Marlin Model 43T (Trap)
and a Remington Model 10T (Target V/R).
I like vintage pump guns too!
I bring the Lindner/ Chas Daly 1912 SBT out too for a run.
Too many to say which one is the best looking.
Maybe it's the Marlin!