I run a Shark filter sitting just high enough that it agitates the top of the water without making a lot of splashing noises (annoying to listen to in the middle of the night). This increases the water surface area, which is good for the fish, and gives the fish a current to play in. Of course, if you have fishes which do not like such currents, you would have the filter lower down and the outflow aimed at the back of the tank so it would bounce off and slow the current rather than aimed into the middle of the tank.
As Goldie mentioned, the dial on the top also enables you to increase or decrease the force of the water flow.