My go to slug is the 3" Rottweil Brenneke, although I do use others from time to time like 2.75" Challengers, and both Winchester and Federal slugs. There is no advantage to the 3" version of the Brennekes, they just happen to be the ones I was able to get at the time, and a 3" shell reduces the gun's capacity by one. I don't do a great deal of shooting with this thing as I prefer a rifle, but it does see regular use throughout the year.
I use the shotgun for a very specific purpose, it is my close to town bear gun, so reaching out to 100 yards is not that important. Shooting prone, the guns prints about 3" @ 50 yards.