One advantage to roller bearings is higher load bearing ability. They spread the weight out over a larger area, instead of just one spot. Probably the most significant other advantages are that they have higher lateral (side load) ability and higher shock load ability. These things are important every time you hit a bump, turn your wheel, or use your brakes. The industry all but abandoned the ball type wheel bearing. Why? Because they are better. Like Longbox (Bill) stated, ball bearings are still being used in cars, but that is in sealed unit bearing applications. My money is on the roller bearings.
Chris
