Placement of the water pump in your pond can be a matter of esthetics and function. Most pumps are submersible units with hose and/or fountain outlets. When you use a pump primarily for the fountain effect (maybe with LED submersible lights to accent the fountain), the pump will need to be placed far enough from the edge of the pond so that any wind coming along cannot blow the water spray out of the pond! You may also have to place the pump on a block to get it close enough to the top of the pond to allow enough of the fountain stem to be exposed to work properly.
The strategy for circulation and filter pumps will be a little different. You will want to place them close to the edge of the pond so it is not difficult to reach them for maintenance. The best place would be inside a pond overflow skimmer box since most of these have a prefilter to prevent large debris from clogging the water pump. The outlet of the water pump should be at the opposite end of the pond to increase overall circulation. Running a hose horizontally will have little effect on the flow rate, but it is best to use the largest size hose possible. The cross circulation will help keep debris suspended to be trapped in the filter system.