Rear locker and center locker have totally separate actions. Rear locker locks the rear axle shafts together for further traction aid. The center locker on a 4th gen, locks the front and rear together changing it from AWD to 4WD. As for which is better suited for you thats totally dependent on your needs. 3rd gen has good aftermarket support, quite a bit cheaper, and are smaller so they fit on narrower trails better. 4th gen has a V8 option, little more room inside for people and for the most part won't have 1,000,000,000 on them. But they will also cost a lot more