A locker, or LSD defiantly. And get yourself a good set of chains. I know its old school, but they do work I the right situations. Mud, snow, anything but rock. Rear tire traction can be increased dramatically. And with a 2wd rig chains on the front will help the front tires drive in the direction the tires are pointed. A major problem when I have been wheeling in 2wd rigs. The front tends to follow down slopes if there is any off camber.

Steve C