I looked at a couple of 21s for sale in a local shop here in Portland, a plain 12 and a plain 20. While they are solid guns with good provenance, the prices these guns fetch cause me to scratch my head a little. (Actually a lot). The receivers are particularly plain and the sculpting of the receiver is rather ungainly to my eye. The wood was plain as well on both guns, particularly the 20, and lacking in refinement, fit and finish. I would put them in the class of the Nitro Special or the plain Ithaca, yet they fetch about 5 times the money. Now I have seen some very beautifully engraved and stocked 21s as well, and those guns are special but they still have that strange receiver line.
I have somewhat the same feeling about Parkers. The lines of the receiver are not great, and in this case it's the hinge pin that is the wart on the gun's face. Again, the high grade guns can be exquisite if you ignore the underlying receiver form. Used plain Parkers don't sell for $3000-5000 though.
The Fox on the other hand is much more elegant, although in this case the engraving on the higher grade guns is a little vulgar (as in lightning bolts etc). I feel these guns are priced in line with their aesthetics and quality.
Just to prove I am not biased against American guns, let me state that I find the "real" Lefevers very attractive both in terms of their underlying lines, and their engraving in all grades. The prices of these guns falls short of their appeal, in my opinion. They are appreciating fast though.
L.C. Smiths I find a little ungainly. The plain guns are not attractive to me with too much unadorned flat metal. The bushed strikers on some guns puzzle me..they have no locking screw and seem to get chewed up. The early Grade 2 guns are much better aesthetically, a huge step up from the field grade. Don't like the stretched engraving style on the Ideal grade at all. The very high grade guns are nice though. Prices seem a little low for a true sidelock.
The Ithaca I find OK to look at even in its basic version, and the engraved guns are very nice. The skinny balls (well they are more like disks) aren't to my taste but not too offensive. Vented rib on some guns is appalling. Don't have a feel for the pricing on these guns since I have never bought or sold one, other than a plain 16 ga damascus gun in nice shape that I struggled to get $700 for.
I like the Remington hammerless even in the most plain version, ESPECIALLY like the engraving on the higher grade guns. These guns are way underpriced to me. Where do you find an ejector gun with a good A&D action, good barrels, for $600-$800? Of course the high grade guns are rare and commensurately priced.
Perhaps it's just me, I am conditioned having cut my teeth on a Greener (not the most svelte gun but it is simple and elegant in its way). I guess one indicator of the popularity of the styling of a gun is the price it will fetch on the market. So that would put me in a minority, when it comes to Win 21s. They must be the most expensive American gun in field grade, by far.