Paper or plastic is of course provide cause people demand it. Its mostly pandering to old timers who like sturdy paper, and ecofreaks that dont have a clue.
On the plus side of plastic, most of it biodegrades when left in sunlight… which is great if you just pitch the baggs out in your yard when your finished with them. Unfortnately, they usually end up in the landfill under a bunch of other trash.
If you think paper is better, it biodegrades when aerobic bacteria eat it, so covering it up with other trash stops it from biodegrading too. And paper takes up 7 times more landfill space that plastic.
If your woried about the trees, dont.
Paper demand doesnt drive the hacking down of forests. Lumber demand does, and the scraps are used paper, or trees are specificly grown for paper.
If your worried about the energy, get a car that gets good gas mileage. You’ll be doing the envoironment a much better favor in the long run.
And as markx points out, re-use it the best of all choices.