I'm a big believer in rifled barrels with sabots.
I've shot both ways and the rifled barrel shoots like...a rifle, within it's effective range. Very repeatable accuracy.
In my limited experience with the smoothbore rifled slugs, they give me about twice the group size.

Big difference in ammo price though. Sabots will empty your pockets quick.
Some guys compromise by shooting rifled slugs in their rifled barrels. To me, it doesn't sound like it should work since the 2 types of rifling would almost certainly be different pitch and might even be a different direction, but I know some that swear by it. The downside is heavily leaded barrels from the steel barrel's rifling cutting into the slug's lead rifling.