Answer:
You can tell whitch wheel is bad because if you turn to that direction you will feel that one side is leaning down more than the other
actually you can use a car jack, and jack up a side, and put your hand on the top of the wheel and bottom of the wheel and try to rock it, if it rocks then the bearing in loose or bad, and you can spin the wheel and if it hard to spin or makes a gring noise then it is bad. some times the axle bolt can be loose check that too.