A bad wheel bearing usually manifests as a growl as you pick up speeds, most audible in the 30-50 MPH range IMO. A bad U-joint could contribute to driveline vibration and cause clunks when the direction of power through the drivetrain reverses (e.g. accelerating or engine braking).
If you hold your foot on the brake and switch between reverse and drive, a thump would imply driveline play. If that's the case you'd need to isolate the location of the worst of it - though I'd go out on a limb and say there's undoubtedly some play in all the major components by now.
You can do some basic tests to determine how much driveline wear you have, and localize it.
Put the rear end of the car in the air so both wheels are suspended. With the transmission still in park, try and turn one of the wheels. If you have a limited-slip differential the tire should stop after minimal rotation. With an open diff (or a limited slip that has worn out clutches) the tire on the other side will spin in the opposite direction. You might need to brace the other tire or find a helper to hold it still (or just to watch other components for movement).
To narrow down the play in the driveline, you would need to watch the halfshafts and driveshaft carefully relative to the motion of the tire to determine which moves (and how much) when you rotate the tire. If the tire moves without the halfshaft moving, it would be a worn out CV joint in the halfshaft at the wheel bearing. If the halfshaft moves but the driveshaft doesn't, pay close attention to the inner segment of the halfshaft at the diff to determine if that end is worn, or if it is worn gears in the diff. Give the same attention to the driveshaft after all the play/slack in the halfshafts/diff have been taken up and the torque of your spinning the wheels is transferred to the driveshaft. If the pinion end of the driveshaft moves but the driveshaft itself does not, it could be the rear U-joint. If the driveshaft moves but the driveshaft yoke does not move, it could be the front U-joint. You could also check the driveshaft by just grabbing it and trying to rotate it, but you'll get more torque to it by turning the wheels.
Put another way, where something that moves meets something that doesn't, there's driveline slack there. Some is to be expected... but a very limited amount, and not in the diff or bearings like U-joints.