I agree rear only, the ATV will be darn near unstoppable anyway. Please check carefully that you have adequate clearance for the chains, especially on the inside of the wheels. My chains hit the brake adjuster wing nuts on my Bayou. I had spacer discs added and now everything fits fine.
After I deflate and install the chains I use some electric fence wire to tie the loose end of the links to the side chains so they aren't flailing around.