A recent paper by Wally Tyner published by Purdue University shows that, at least for Corn Belt states (like Indiana), corn stover could be a better cellulosic ethanol
source than switchgrass. The paper considers the cost and prospective profits of whether a farmer could decide to plant and sell corn and corn stover, or plant switchgrass. The answer is clear to the author: corn is more productive, the soil quality is low, in which case switchgrass becomes the winner. There is also a consideration about the location of ethanol plants: they need to be near the feedstock, because corn is easily transported but corn stover and switchgrass are not.
Although you can check the complete report
for the all the figures, take this statement by Tyner as an example of his summary: "With $6 and higher per bushel corn it [cellulosic ethanol] is already very close economically. And since the federal Renewable Fuels Standard calls for the production of 36 billion gallons of ethanol by 2022, of which 16 billion gallons have to be cellulose, cellulosic ethanol will advance."