Many of them come with some sort of diffuser/deflector thing that you can use to aim the water at the top. My penguins have been running 10 years at least, and my 550 is in a 75 grow out tank. It should be OK in the 20, they stay out of the blast at the top.
Actually what I found to work pretty decent is the Aquaclear 30 powerhead with the filter attachment.. I was using one on my 20 long for awhile but was also run an AC 50 and didnt need that much filtration so I removed it..
I like the ViaAqua powerheads. The cheapest one is like $6 at a certain large online retailer and pumps somewhere like 80gph. I use one in a 20 gallon I have for a growout. I have several other larger of their pumps as well.
Just checked and it looks like they don't have the smallest one listed anymore, pretty sure I had one smaller than the 152gph I see listed. Hrm...still great pumps and cheaper than any others you will find.
Have you tried the tetra whisper? I CANNOT hear it, at all. I have one driving the sponge on my 29 gallon tank. It is absolutely SILENT, and cheaper than a powerhead, worth a try. Maybe your LFS will plug one in for you. I set mine under the cabinet of my tank, right on the wood, not a peep from it. I can't even hear it putting my ear next to it, if it weren't for the bubbles I'd have to put my hand on it to know it's working.