A Rena xP3 would be great for a 55 gallon. I do agree that AquaClears are superior filters in design in regards to capacity but they are not as good in materials - the plastic cover easily cracks and are not as bendable as the Whispers. In my experience, if your power goes on and off, the Whisper will flow again but the AquaClear will not. But even the largest AquaClear 500/110 is whisper quiet while Whispers are quiet only up to model 40. I highly recommend a Rena or Eheim canister over both HOBs, the Rena's operation, instructions, and accessories are perfect while the Eheim has much more capacity.