It depends on how much you want to spend and how it will last. I to put out corn. Cob is cheaper and will last longer before they have to work on it to get it. Kernal will get eat up in no time and cost a little more. Whatever you put out spread it around some so more than 1 or 2 deer can eat at the same time. The more the merrier I say. I put out 2 5gal. buckets full of kernal the other day at about noon and by 6:00 it was gone. Cobs been there a week with some left.
For the opponents. They are going to go eat in the corn field or off my pile, I ain' t drugging them. The sport is also finding them, positioning the stand in relation to bedding/trails properly, knowing when they are feeding and being able to make a clean kill shot.