This has been covered more than once, check the archives for info. A few fast points, tho...
Practically any reliable shotgun holding two or more shells will do an excellent job IN TRAINED HANDS. The software is much more important than the hardware.
Any of the Big 4 pumps will work very well, and so will some autos and doubles.
Some 20 gauges will kick harder than some 12s. It's a combo of fit,ammo, action, and technique.
Some folks do not shoot a shotgun well, ever. I suggest you make some alternate arrangements for your wife. Mrs McC doesn't like or shoot shotguns, neither does Daughter. They have other tools available, mostly in 38 Special. The HD 870 is mine alone.
Finally, after you've obtained a shotgun, resist the siren lure and spend your money on ammo, lessons, and range fees instead of bellsnwhistles. Those MAY come in handy later. And shoot the thing, at clays, landfill rats or whatever. The shotgun's its own best learning aid.
Good luck and good shooting...