Sponge filters are good. For a 20L I used a large filter hooked up to a Tetra Whisper 100 pump. Worked well in a shrimp only setup. I tried a corner filter too and it worked good as well. I always wanted to try a corner HMF filter but never have.
Question is why are you wanting to ditch the HOB? Sponge filters are pretty obtrusive in the tank and I actually dislike all the bubbles but they are awesome for shrimp. HOB gives the freedom of some media options and better water flow and they aren't any more ugly on a tank than a sponge filter is in a tank.
If you are wanting to clean up the looks maybe check out some canister filter options.
Ditching it do to space outside of tank... Need to be able to get closer to wall... I no I will miss the sheer amount of water my HOB can filter per hour. But I also have a pretty nice clean up grew with shrimp... And found a place that actually has ottos so that will help also.
Also upgraded my lighting so I'm hoping the healthier live plants will also help with the difference...