What would be the ideal filter for a 55-gallon, live-planted aquarium? It will house 4 angelfish and maybe a few small peaceful tetra. This is for my brother-in-law's tank.
If money is not an issue I can not recommend the Eheim 2126 or 2128 filters enough.
First, on a planted tank you definitely want a canister filter. Secondly the 2126 or 2128 integrates the heater internally which eliminates the need to have an intake one and adds the overall look of the tank.