Aquaclear are easy to use, quiet, and work great. I have also used Emperors and Penguins and would recommend them. But after buying a couple AC 70's, those are the only HOB's I would buy myself.
For tanks under 30 gallons, I prefer the super easy maintenance and the bio-filtration effectiveness of a Penguin. Between 30-75 gallons, I prefer ACs
AquaClear filters are the best HOB filter ever made. Emperors are a close second. Been running both for many years.
I am in favor of simplicity in filtration. Since WC is my ultimate filtration, I don't need any filters more complex than sponge filter and HOBs. Canister and wet and dry are therefore off my list because they are complex, in set up; the more complex they are, the more things can go wrong and I believe in Murphy law that they will. However, sponge filter is ugly, so I only use them in my grow out tank. In my show tanks, including my big 125g, I use multiple HOBs exclusively. I know majority of people prefer AC, but my preference is Marineland Penguen, not the Emperer series because I dislike the complexity of the jet spray. I have no love for the biowheel in Penquen either, so I just run mine without the BW. I prefer Penquen over AC because the box is thinner so I can locate my tank closer to the wall and I deslike cleaning up gunk up sponge. Additionally, the upward flow through the sponge in AC adds complexity that gunk up sponge has the potential to pop up and drip water to the ground.
