I love chains. Granted, they are a pain in the azz to put on, but they make such an incredible difference. Put all four sets of chains on if you've got four. If you don't have four, get more. They are useful tools, why not have a full set?
By the way, going to elk camp this year the leader had two sets of chains on his front tires and got stuck going up hill on the north side of the mountain. I had four sets of chains and was still mobile. I was able to pull him out and then we backed down off the mountain until we had a hair-pin turn where we could execute a touchy about-face. If you have more than one vehicle and at least one vehicle does not have four sets of chains, let the vehicle(s) with four chained tires bring up the rear. If the lead vehicles get stuck, hopefully the rear vehicles are still mobile and can render assistance. Going down the mountain -- like at the end of a hunt after snow has happened while you were in elk camp -- the order might best be reversed. The guys with four chains might ought to be on the downhill side so they can hitch up and pull. Of course, leaving you might find that even the guys with four chains get stuck. No advice for that situation, other than to be sure to take a sky hook with you . . .