Based on my experience/my guns
NEF Tracker II 12 guage rifled barrel - 3" Activ slugs (No longer made, but I've stocked up on them)
Mossberg 9200 autoloader, 24" rifled slug barrel (no longer made, found it in a now out of business hole in the wall gun shop, the buttstock has the nicest wood I've ever seen on a Mossberg) - Best load - 2-3/4 Winchester Partition Supremes, also shoots 3" Brenneke Gold well, but even with rear sight at lowest position shoots 3" high at 100 yards. Also does well with my roll your own lyman mold sabot loads using standard wad as the sabot. My wife likes to use it with the Brenneke 2-3/4 KO slugs (and they're cheap, too)
Mossberg 695 bolt action 12 guage rifled barrel - I used the Lightfield EXPs in 3" until Winchester introduced the 12 guage partition in 3". The Winchester 2-3/4 partition loads stunk. The first Hornady loads stunk. All editions of Rem copper solids stunk. It also shoots the Brenneke gold 3" and Brenneke 2-3/4 KO well. The KO slug is $1.99 for a box of 5, so I can practice with it. It also shoots the hand loaded lyman sabot loads well, but only for about 5-10 shots and then the wads used for a sabot really gum up the rifling.