What are you using your dewatering pump for? Is it for construction, municipal use, or for mining? Or is it for something entirely different?
The application will determine the type, and the size of the pump required. Dewatering pumps are versatile. They can tackle a myriad of tasks. They can tackle grey water flooding and are excellent for clearing flooded areas. A good example is excavation sites. Find out how high and how far you need to pump the water. This is your deciding factor.
Another question to ask is if the pumped water contains solid material or not.