When it comes to choosing a frame for your BMX bike, it really only comes down to what you intend on doing with your bike.
Most frames are either made of aluminum or steel. Both of which has advantages and disadvantages.
Steel in a highly durable material and therefore excellent for powerful and risky stunts. Aluminum on the other hand is a lighter material, which is still durable, but not as much as steel. This makes frames of aluminum slightly smarter for the youngest and smallest of freestyle BMX riders.
However, if youre a professional or advanced rider that needs something very strong for the types of stunts you can pull off, then youre going to be better suited with a frame of steel.