I have played with, researched, shot, reloaded, cast, and recovered (a few) slugs of many types for many years.(I typed "tears" which might be true). I am in no way an expert but in my experience modified has performed as well or better than the imp cylinder that most gunmakers traditionally put on their fixed choke smoothbores. Not all, but most for me. I have an 1100 barrel with an ugly Polychoke that shoots cheap Fosters as well to sixty yards as my old Hastings barrel did with Lightfields. The Foster slugs were designed undersize and the "rifling" ribs were made to squeeze through tighter chokes.
My normal recommendation to beginners with a smoothbore is to try Federal Truball or Brenneke slugs first. Some shotguns shoot great with Foster slugs regardless of choke. My first few deer were taken with my TB 870 and an 18" riot barrel I put rifle sights on.
I quit fooling around three years ago and bought a 220 Savage, the closest thing to a rifle I can use in IL.