Wigeon or Bluebills due to visibility and they are confidence on teh Columbia in my opinion because those are the main birds that raft up and there are a lot of them all over.. any birds will decoy to Mallards, Wigeon, and Bluebills..

someone also said coots, those are a great confidence type decoy.. any time you see a raft of ducks, a majority of them are coots... ducks tend to lean towards them..