The Emperor's are good filters, as well as the TetraTec's, which can also keep your temperature very stable by adding the optional heater module. Or, if you consider a canister filter, Fluval makes very good canister filters, although they can sometimes be a hassles to clean or change filter media, but overall work very well. But, these are just the tip of the iceberg in filtering. Are you planning on having sand and rock in your tank? If so, you may want to consider simply adding additional sand and rock to make your sand bed 4-6" deep and around 75# of rock, and get a good protein skimmer. This would be all you would need for filtering, as the rock and sand contain the bacteria needed to process waste products. With a good protein skimmer and good powerheads for movement, you would have a complete filtering system. In a 55, this would be my suggestion, as the additional rock and sand required to make it would not be any more expensive than buying a power filter, and you are likely to end up with that much rock anyway. HTH.