To decide on the best one for you, you'll need to understand the sum of water needing cleaned and get one with a motor that is going to do the most work for your pond in the 3 hour time limit you've got. A pond isn't something which is simple to move if, in a couple of years, you don't like its location. Most ponds aren't too deep, but they generally have rocks that may easily render a child unconscious in the event the child should happen to slip and fall.