Mike I guess it depends on what you are looking for??
If you are looking to decoy and to bring in a mature buck, I then would use a buck decoy. When to use it? Pre Rut (Seeking or Searching Phase)IMO is the best time, but Peak and on the tail end can also be productive. I tend to like decoys that have motion. I like motion for two reasons. One it helps to ease the does a lil bit around you. Decoying is a love /hate relationship and most times what wrecks a hunt or a set is not a buck but a weary old doe. This has happened more than I would like to admit for me.
Secondly I like motion in my decoy in case that bruiser hangs up just outside of bow range like they usually do. Sometimes motion at the right time can make that deer commit.
I do use them on food sources but this is often where the love/hate relationship can form. I have had numerous mature shooter bucks on the field edge but will not come out or commit to my decoy because a doe is out in the field stomping at my decoy.
Travel pinch points with open fields is my favorite spot to use them as you are set up on a travel pinch point that bucks often use during the pre rut or searching phase. Also the does never really stop and check things out as they just kind of move through or get out of there if they don’t like it. Secondly the open field part allows a lot of area to see your decoy.
Also IMO bucks all have different personalities and those moods can change by the day even the hour. Just because one buck does not come in to the decoy, does not mean the next one will not. Perhaps the first buck just got his
kicked. He may not be in the mood to try again just yet. I truly believe some bucks just are not fighters and are just a little bit more of a loaner then others. Just remember it is not always the biggest racked buck that rules the woods, it is usually the one with the biggest attitude! Also effectiveness may depend on your buck to doe ratio and your competition for does??? When all the stars align and that buck comes walking in sideways all bristled up licking his chops, there is no better feeling in the world IMO. 
I would love to see the DSD Decoy WF! Let me know when it comes out! 