If this is your first 4x4, you don't need either yet. Lockers are great, but you really need to learn to wheel w/o one first. Right now I would invest the money in rocksliders, good front and rear bumpers, and recovery equipment. Once you have a lot of seat experience you will have a better idea of what you like to do with your rig, and then build accordingly. Building 4x4's can get expensive really quick, so you only want to pay for stuff you really need.

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed