front ..
if your front tires climb up then your rear will fallow
if u lock the rear and the front cant climb then the rear will just keep pushing and the front will still not climb
somone mentioned going up a hill blah blah blah if your weight is on the rear good chances both tires will be loaded with that weight so youll have power to both tires
lock the front its the smarter choice
if it doens't grenade
if your fronts have traction and your rears don't you are putting added strain on the front diff. a D30..... a low pinion 30. because the rear cannot push the front end up and over and the rear is now pulling the whole jeep intead of pushing.
so you will be asking your front end, on the weaker axle to 'pull' instead of push over an obstacle. bring spare shafts..............
so, that said, D44 rear locker hands down. lock the stronger axle..............
apeman is right. rear locker, you can go in 2wd further than most open diffed rigs..............