Aluminum. A lot of college players have problems going from college to the minors and then on to the pros because of the switch from aluminum bats to wooden bats.
A baseball flys further w/ an aluminum bat. it is estimated that a ball can fly on average 50ft further w/ an aluminum bat
Aluminum bats out perform wooden bats. They don't use aluminum in the Major League because every ball would be hit out of the park. The home run records would be obliterated.
It depends on who swings the bat. If Albert Pujols were to use a wooden bat and then use an aluminum bat the ball would fly furthest with the aluminum bat because they are lighter and the ball jumps of the bat.
In terms of physics, the aluminum bat would send a ball significantly further. Wood is denser than aluminum, meaning that you can have a much lighter aluminum bat but just as much power. In other words, you can swing an aluminum bat faster than a wood bat of the same mass. Aluminum bats are also much more solid because they're made up of uniform material, as opposed to wood which has variations in density and strength throughout. There's a great statistical comparison/analysis at the following link:
