Locker in the rear is much, much more effective, than an LSD in the front. Always get traction to the rear, first, then worry about the front.

Reason is, if you're climbing a hill, or climbing a rock, the truck is gonna' be on an angle, nose high. Which means there's more weight on the rear axle than on the front, when the weight shifts. So you're naturally going to have more traction available at the rear than at the front. Doesn't do you any good to have both front wheels turning, if there's not enough weight on them to pull the truck forward.