If I could have just one it would be the TDC in 12ga. You can change chokes to suit a lot of hunting situations. I like to sight down the rib as well. You can also use clamp on sights on the rib, so with an extra full choke it's a turkey getter and CYL choke shooting foster slugs it's a short range deer gun.
If I had the option of adding accessory barrels The 1st would be a 22" mod choke for my day to day walking around/truck/hd gun. That short barrel is just so handi, quick to the shoulder and easy to manuver.