From everything I've read/heard, I would agree with Cab that the heavier one will absorb vibrations/harmonics better than the lighter one. Solid aluminum hubs with are said to contribute to broken cranks and other problems due to no dampening properties. An ideal set-up would be an aluminum center with a steel outer ring which would provide the best of both worlds - lighter weight for faster reving with a heavier outer ring to dampen the vibrations and harmonics. But since the benefits would be minimal with an aluminum center, I simply use a quality steel/steel balancer for durability. (Weight reduction closer to the center of rotation provides less benefit than weight removed further out from the center.)