In the fall the birds will generally be segregated to groups of hens with young birds and bachelor groups. If you are hunting for toms then I would recommend tom or jake decoys, and probably have a few of them in the fall.
In fall, generally you're going to want to spread a flock of turkeys out and call them in like the mother hen would. I'd set up a hen decoy and perhaps a couple young turkey decoys for the most success.
I have never used decoys in the fall because I think it is more dangerous if your state allows rifles to be used in the fall season. That being said a hen decoy with a couple of others would probably work well because it is the old hen who assembles the flock after they are busted.