Baseball bats MUST have either a USA Baseball, BPF 1.15, or BBCOR 0.50 sticker on it for it to be valid for game use. Which bat hits the best? Generally speaking, a BPF 1.15 have more pop than a BBCOR 0.50 (generally only used by bigger 7th graders and 8th graders anyways), which will have more 'pop' than a USA Baseball bat. Will Taylor started the "Bat Bros" on YouTube. Bat Bros does a FANTASTIC job of reviewing individual brands of bats on their videos.
To calculate the weight of a bat, take the length and subtract the 'drop' or minus from it. For example, if you see a 30 inch bat, and it has a "-8" on the barrel, you know that the bat weighs 22 ounces. See the chart below for suggested lengths. A rule of thumb is a child should be able to hold the bat with their dominant hand out at a straight 90 degree angle from the side of their body at shoulder height without it dropping down at all for a full 30 seconds for it to be the correct weight. We suggest not buying a bat that your child can 'grow into'. We want the players to be able to do some damage to a baseball NOW, and not be late on their swing because the weight is too heavy for them.
Coach Eric (Simantel) has had luck over the years using Sideline Swap. He's been able to re-sell old bats there and reinvest in newer bats that may have only been used by another player for only season in another part of the country.