i have had excellent results with winchester supreme sabots very accurate to almost 150yds. they're in a black box, black shell, silver end and slug. they have a few types but of the supremes but those have dropped deer 120+ yds for me.
Slug guns are tricky. Every gun and every barrel is different. Two of the same guns with the same barrels might like two completely different slugs. The one slug I have found to be accurate out of all 3 of my slug guns is the 2 3/4" lightfield hybrid exp. Mine are all 12ga but here is a link to the 20ga version.
The Lightfield is a good slug! I have had really good luck with Hornady SST's and Federals with Barnes Expanders. Best thing to do is shoot several boxes and see what your gun likes. I have a smooth bore 20ga. that loves cheap Winchester Super X's. I killed a deer at 160 yards with it!