I'm betting you already know the answer but for those who might not be sure, check out:I think of it this way totally dry wood which do you get the most heat from a 1000 lbs of Oak or a 1000 lbs of cotton wood ?
Kash
http://worldforestindustries.com/forest-biofuel/firewood/firewood-btu-ratings/Per that site, oak beats cottonwood almost 2:1.