Anything with a regulator and a plenum, maybe 2 regulators like on the new guns like the Maverick and the new M3 Impact, for that final very fine tuning to get things just right.
IMO you generally have to think about what distance you will shoot at, and if thats long for any given caliber you probably want to shoot slugs.
So if you want to shoot slugs it come down to, do you want to shoot lighter slugs, or the heavy ones, if the heavy you need a updated liner for that, pellets & lighter slugs shoot fine from the ordinary STX or Superior liners as i understand it.
Personally i would not go all slugs at the moment as availability at any caliber is a bit iffy as i understand it, so i would preserve the option to have a little fun with pellets too.
No matter the barrel and ammo, if you shoot it wrong, it will not be good.