well for starters, corn is not nearly environmentally stable, it requires higher inputs more labor and the market for corn is HUGE!. however it is crop people know how to grow, it is more energey dense and can ship easier in regards to shelled corn versus whole stalk or even corn fodder. on the other hand switch grass is much more environmentally stable requires much less inputs and the purity can be quiestionable when the source is coming from CRP, BUT there is a LOT of land coming out of CRP 150 MILLION acres in the US, and people are looking for sustainable ways to farm this land as most it is not suitable for row crops. anyways, on a last note switch grass coming from CRP can produce in the ballpark 3-4 ton/acre, 6 if your lucky. Elephant Grass on the other can wil produce 10 ton/acre no problem and 14 if you manage it correctly. However it's an invasive species, is hard to plant and grow upwards of 14 feet which makes it somewhat difficult to handle. check out University Illisnois to learn more about Elephant Grass; google Bill Johnson Manager-biofuels division of Aliant Energy to learn more about switch grass.
P.S. One other source the people at Aliant are looking at is forestry products, mainly the scrub and brush parts which they actually were burning but can also be made into ethanol.
I am senior majoring in Animal Science and have seen multiple people talk about this subject in Nutrient management and Forage Production classes at the University of Wisconsin-Platteville