I've tried a little bit of everything in my spread at one time or another: Canada goose, teal, crow, great blue heron.....can't really say they worked or not. I hunt a public area that receives a LOT of pressure, so once something becomes popular, everyone starts using it and the birds wise up rather quickly (a good example of this is the mojo ducks; when they first came out, guys who were using them were slaying ducks....then when everyone had one, they didn't seem to work as well).
The one thing that I have had repeatable success with is a string of 8 goldeneye decoys. I set them in a line off of my main "J", "C", "V", or whatever. I think they work for two reasons: 1.) they have a lot of white on them, so ducks can see them from a fair distance away and2.) they area a common bird in the area, but not too many duck hunters use goldeneyes in thier spread. I think heavily hunted birds cannot only count (I think that they won't come down if 24 or 36 decoys are present), but that if they see a bunch of teal off to the side, they get hinky!
"If your dog thinks you're the greatest, don't go seeking a second opinion!"