The answer to this question is going to vary significantly by both geographic location and by the quality of soil you have to work with. RUR soybeans might be the best answer in southern IL, but would be a complete failure on sandy-land plots in hotter or colder climates.
If the question is about a single seed variety, then I reject the premise: Planting a mono-culture food plot is never the best choice for wildlife. The mix Native Hunter mentioned, adjusted for your local region, is absolutely the way to go. The varieties will change as you go north/south from his Leopold Landscape in the Bluegrass state, but the premise remains the same.
On my small properties in northern Michigan, the foundation is a mix of winter rye, red clover, alsike clover and chicory. Where the soils are better, or have been improved, you can mix in oats and a forage radish. Minimal tillage and a mix of cereal grains, legumes and other plant types are impossible to beat, especially if your plot is intended to do more than just kill a whitetail deer.