Speaking of 12 Gauge only...
I've borrowed and shot a Superposed trap gun for a few months. Tried to buy it off the guy but he wouldn't sell because he has a hand injury that affects his trigger finger, and it's one of the few guns that doesn't double on him.
It's a fine gun.
Due to the ancient receiver design, it's pretty heavy and very bulky, though, and I wouldn't want it for much besides trap. It's durable, but you pay for that in weight. I wouldn't want the field version (I can't stand the cheap Japanese knock-off Browning makes now, either -- the Citori that is). It was also made long before steel shot was invented, should you want to use it for anything that requires non-toxic shot.
A Superposed in 20 and/or 28 is a dreamy little gun. The receiver scales down so much between 12 and 20, it's a whole different shotgun. A Superposed in 20 is one of those things I'll try to buy if I ever see it for a sane price.
But in 12, I'll take a new Beretta 686 White Onyx any day of the week, for all-around shooting. I got mine for $1500 NIB about 6 months ago. I've loved it since, and it's not like it's the only shotgun I own or have shot. In 12, though, it's my hands-down favorite. I know that the cool kids insist on a gun that's at least 20 years old, but I know what I like to shoot. The rust-resistant receiver is also a big plus. I've rusted a blue O/U with sweat.
That's all my personal preference. Some people really love Citoris. I prefer a sleeker, lighter gun (the Beretta is a pound lighter in 12 Gauge). I'd skip the Rugers and Citoris, though I have shot decently with the Rugers. I want a gun I can use in the field, and both those guns weigh 8 lbs. Too heavy for anything but trap and waterfowl.
Again, in 20, things change a lot.
Regardless, if you can, try before you buy. Some guns may work for you and not me, or vice versa.