I was looking into the same thing for my 870 express. I would stick with my smoothbore, but want something shorter, as my current bbl is 28". So a Remington fully rifled bbl w/ sights is ~190$, while a Hastings fully rifled bbl w/ sights is ~215-230$. Both around 20" bbl's... Its really up too you since the price difference isnt too much, but keep asking and maybe somone who has tried both could tell you pros and cons... I mean, your shooting a shotgun slug, from a SHOTGUN, so accuracy just over 75 yds is tops right? I would just use your one barrel for both slugs and shells, and buy a 5" rifled choke tube maybe.
I still want a ~20" bbl. im thinking smoothbore, too so it'll be good for woods use, with either buckshot, and a rifled choke tube for the slugs if i choose too go that way...