The two main motor styles are hub-drive (motor in the front or rear hub of the bike) and mid-drive (motor in the pedal axle area). Hub-drives are easier to ride for beginner cyclists as it does not matter what gear you are in. They are also good in flat and moderate terrain. Mid-drives take a bit more skill to ride and constant shifting of gears, but offer much better performance in steep and offroad terrain because the motor drives through the gears train, so, when you change down, the motor changes down too. Make sure you a clear with how you want to use your ebike, so you get the best motor system to suit your needs.