“In-line” pumps provide the “most bang for the buck” in two ways. For one, the purchase price is quite reasonable for the high volume of water being pumped. But even more importantly, these pumps dramatically outperform typical submersible pumps, cutting electrical costs two to three times. Since electrical costs for a large pond can easily run from thirty to one hundred dollars a month, choosing the most energy-efficient pump is tremendously important.
However, if you need a lot of “head,” that is, if you are pumping to a height of more than say, seven or eight feet, or if you must pull the water (not “push”, for in-line pumps push water fine but don’t pull well) a long distance from the pond to a skimmer located far away, then these pumps probably won’t work for you.