Along the lines of which is better for the environment – paper or plastic bags is the "which is better for the environment" paper or digital format for documents. Bet you are leaning towards digital — I am.
" … main selling points … of eReaders is that they are greener than print. … common view held by consumers … is that going digital means going green and saving trees. Many are in for a rude awakening. … subjected to ‘cradle-to-cradle’ life cycle analysis, eReading is not nearly as green as many naively assume it is." 
" … Computers, eReaders, and cell phones don’t grow on trees and their spiraling requirement for energy is unsustainable."
" … digital devices require a constant flow of electrons that predominately come from the combustion of coal, and at the end of their all-too-short useful lives electronics have become the single largest stream of toxic waste created by man…."
Via: ZDNet LINK