Steel shoes have better metallic memory than aluminum. That is, they do absorb some shock and concussion, and spring back to shape better than aluminum shoes do. Aluminum shoes will tend to spread in the heels more than steel ones do, because as they undergo stress, they do not retain their shape as well, due to the lack of metallic memory. Which isn’t usually a huge deal in the hunter ring, but can become so in certain instances. The lack of weight with an aluminum shoe can be helpful in keeping action lower to the ground, but it is a trade off with the increased wear on the softer metal requiring more often shoeing. The constant shoeing done at racetracks can be a source of foot trouble, not enough growth to put nails into new horn makes for less secure shoes. Lack of growth of hooves is endemic at racetracks, as are tender feet.
What is going to work best for any particular horse is individual to that horse, his feet, his environment and his workload.