One of the main advantages of a bmx bike is the smaller wheels and frame compared to a mountain bike, this allows the rider to have a lot more control over the bike when jumping and doing tricks. If you have ever tried doing tricks on a mountain bike you would understand how much suited bmx bikes are for doing tricks.
Bmx is also split up into a few different categories with specific bikes for each catergory.
Bmx Freestyle – Freestyle Bmx is called this for a reason when riding at the skate park or dirt jumps you have complete control over the style of riding and tricks you do there are no set rules.

Bmx Race – Bmx racing is were bmx all came from race bike frames are normally made from alloy not chromoly steel like freestyle bmx bikes these allows them to be a lot lighter and racers also run the bigger sprockets due to the strain on the chaing when raing

Bmx Flatland - Bmx Flatland has also been around from the early days of bmx this is where tricks are performed on the flat ground this is one of the most difficult styles of bmx to learn as it takes hours of practice

So when choosing what sort of bmx bike to buy you should always consult your local bike shop for the best suited bike for you.