The newer Jeeps actually have both! It's an improvement over AWD and they call it "Active Drive". It engages/disengages the center differential (4WD) as needed

The newer Jeeps actually have both! It's an improvement over AWD and they call it "Active Drive". It engages/disengages the center differential (4WD) as needed automatically, but can also transfer power to be greater in the front or rear as desired - with presets for 60/40 and 40/60 rear/front power. (Sport mode, Mud/Snow) It's also got traction control w/ ABS, and it uses the brake locking differential technique on each axle as the article describes in advanced AWD systems. Of course they have different variations, one of which also has locking differentials on top of everything else. It's amazing to drive. It's all fully automatic too.