All you really "see" with an HOB is the top of the filter, and the pickup tube, given that you have a proper background on the back glass....all of my tanks have painted (black) back glass, so you see none of the equipment/cords behind the glass
The filter should always be based on the needs of the fish for water movement and the "filtration" aspects. Water movement affects fish whether negatively or positively. The actual "filtration" involves mechanical to keep the water clear, and then biological/chemical to keep the water clean. These are different things.
You mention plants, so right off there is no real need for biological/chemical filtration, and it will be counter-productive if too much. You may or may not need mechanical filtration depending upon the setup. But the water movement has to always be kept in mind.
This all assumes the stocking will not be beyond what can easily be supported by the system (volume, plants, species).
The appearance of the filter is somewhat important, but not if the needs of the fish are being ignored in order to have a better visual appearance for the aquarist. My 29g tanks over the years had a dual sponge filter; they had plants including floating plants, and small fish that cannot deal with water currents.