i think research is pointing towards switchgrass as the best source for ethanol biofuel: it grows incredibly fast and is not picky when it comes to its soil and environment. obviously, crop yield is higher in optimal conditions, but being a weed, switchgrass is more robust than say corn and does not require fertilizer. not to mention, switchgrass could be used as its own fuel for boilers in the production process, unlike corn which would require coal
both crops require farm equipment running on dino to be harvested and have the initial plots plowed out, but the amount of pollution left at the end of ethanol production with switchgrass is far less than that with corn