Submersible pumps come in two styles: utility and trash pumps.
The type of water you'll be moving will determine which type of pump you need.
If you're just removing water, a utility pump will work.
But if you need to move water with solids, debris or sand in it, go with a trash pump.
Submersible Utility Pumps

Utility pumps are versatile pieces of equipment. You can remove standing water, empty clogged sinks or drain window wells and other areas. The inlet size will dictate how quickly you can remove the water. The more water the pump can take at a time, the faster it can disperse it.
Look for a utility pump with a float switch. This makes the use more automatic, as the float will kick the pump on and off so you don't have to watch it. Without a float, the pump will run continuously. In this case, once all the water has been removed and the pump continues to run, it can overheat and breakdown.
If you need to remove water with debris and solids in it, get a trash pump instead.
Submersible Trash Pumps

If your home gets flooded and the water has lots of silt and sand in it, a normal utility pump would get jammed up with the debris. This is where a trash pump comes in.
Using a heavy duty impeller, the centrifugal force shoots the water and debris out of the pump. Just like utility pumps, a trash pump with a float switch will be your best bet. This way you don't have to watch the pump and turn it off once all the water has been removed.
These pumps are more expensive than utility pumps, but are essential if you need to remove dirty water. This most often is the result of river or ocean related flooding.