Filter flows

In the past I have always used undergravel filters but now I have a sponge filter. Experimenting with the different types of flow I cant decide which is best. The pump is very powerful and pumped out a strong current and i cant see a way of turning it down. Is it better to have an underwater current or to use the bar above the water and have the water agitate the surface? What are the benefits and pitfalls of either method?
Thanks

Misopeenut my filter sits on the edge of the glass just under the water level and you can have it either blowing a current through the water or have it dropping water onto the water below. Then you take the sponge out of the filter ever so often and clean it. I want to keep quite slow swimming fish and wondered if maybe the current was too strong and whether having water splashing from above would be better for them?