Below are the explanations of the different hydroponic systems.
Nutrient Film Technique
Nutrient Film Technique is a completely medium free system. Typically, the roots sit suspended in long slightly sloped irrigation channels, with nutrient water flowing through the raised end, allowing a natural flow over the root system. The water is in a form of a thin layer flowing to the lower end of the channel where the water is returned to the reservoir to be reused again. Feed schedules are sometimes run in 15 min on 15 min off intervals however the traditional method is to keep a continual flow
Aeroponics
Aeroponics is a method of growing in which the root system is left to freely suspend in a reservoir. Nutrients and water are introduced in the form of a fine mist, created from spray jets/nozzles and a high pressure water pump which generally operates 24 hours a day. The plants themselves sit in net pots filled with your choice of medium. Although it is considered one of the newer methods of hydroponics, it is often considered the fastest growing methods.
Wick
The wick growing method is considered to be the most basic and easiest to setup hydroponic growing system. There are many styles of wicks but they all surround a principle of having a wick to automatically draw water up as needed by the plant. Water and nutrients are provided by the wick to the medium when needed. Which allows your plant to feed as required with the wick automatically re-hydrating the medium.
Ebb and Flow
One area where ebb and flow stands out as different is, the fact that water and nutrients are introduced to the root system from beneath instead of from the top. This allows the root zone to flood to a predetermined and controlled level and is then allowed to drain back into the reservoir. This is all controlled by a pump, timer and a drain/overflow that run on an alternating cycle , the pump runs for whatever period of time you decide, allowing it to reach the desired water level , with the overflow handling any "extra water" that may go through in that time and then the system is given enough time to drain out before refilling again.