Almost all of the new aluminum bats will give you the same benefits.  They are all made relatively similar and will give you about the same amount of “pop”.   You want your player to choose at bat that he can comfortably swing at a weight that doesn’t cause him to compromise his mechanics.

At a younger age, players typically have strength issues for which I would err on the side of bat that is shorter in length and a little bit lighter.  As a player begins to mature and begins adding some muscle to his frame, he can test out different sizes to see if he can handle an increase in size.

As far as make and model are concerned, I have always been a fan of one-piece bats.  Two-piece bats had too much flex for my comfort level, however, I know plenty of players love the two piece option.

As far as wood bats are concerned, I would suggest anything maple.  Maple bats are easier to maintain and often add a little more bang for your buck.  As with anything, there are lower and higher-grade models, but most maple bats are durable and can last a long time.

It is best to have you player test out different makes and models to find a bat that is best fits his strength and style.