I would say the wearer makes the gun in this case. Weapons can be beautiful on their own, but hardly sexy. A pretty man or woman in the right clothes can be made sexy with the addition of a gun though.
On it's own I'm quite fond of the Spas-12, and sleeker pistols. Rifles, especially scoped one's are really nice too.
Of course I also have to mention that a steampunkish revolver polished to a silver shine with brass inlays is better than anything else though. (And my automatic gauss rifle, but I actually don't have the real thing yet, just a shiny blueprint)