RE: slug barrelll or rifled choke tube
Ultimately, your greatest accuracy is going to be with a barrel that is rifled from chamber to muzzle. Lots of todays advanced slugs need that rifling to stabilize. A rifled choke will allow you to shoot these advanced sabots and slugs by imparting just a bit of spin at the muzzle end of a cylinder barrel to stabilize the slug. What it may mean in the end is that your choices as far as what slugs to shoot might be limited by those that only need that small impartment of rifling to stabilize.
Personally, I was faced with the same question during the off season. I chose to buy the barrel and I'm glad I did. I can now shoot a miriad of the new slugs with some accuracy and a few with great accuracy. I shot yesterday, and I'm putting up 2.5-4" groups at 100 yards with Remington Buckhammers at 1 1/4 oz. The best part about that is that it's stabilized and zeroed at 25, 2.5" high at 50, 1.5-2" high at 75 and back dead on at 100..... very little bullet travel = more confidence in the field.