Don't get me wrong, there is a good feeling associated with coming home with those brand spanking new Greenhead Gear decoys. The paint is new and glorious, the bodies are in great shape, and you get to start from scratch. Then the first 5 hunts happen and all that is a long ago memory!
I am a big proponent of a realistic duck decoy spread. Inherent in this is likely many different brands of decoys. They all have their slightly different look and this more mimics the real world. This is where buying a bunch of used decoys shines. It allows you to find a few decoys of each brand and species at a discounted price. I might suggest looking into some G&H duck decoys as they are notorious for being durable and holding 
their paint well, but all of the major brands are likely to be in good shape. It is also a great way to add a few of a different species to your spread. I have found pintail decoys to be especially effective for decoy wary ducks.
So for those looking to expand their spread or those on a tight budget, I would encourage you to look at some used decoys.