LED pool lighting technology has come a long long way in the last 5 years. In fact LED lights are revolutionising all lighting applications including swimming pools. They are now cost effective to produce, have high light output and use a fraction of the amount of energy as traditional lights. There really is no good reason not to choose LED lights.
LED swimming pool lights are made up of many LEDs inside them. Quality LED pool lights illuminate the pool much more evenly than halogen lights. Halogen lights give more focused light (think of a torch beam), whereas LED pool lights spread the light more giving a glowing effect.