That one depends on some many things. What do you need or expect?i would like to know what you experienced aquarists think i the all time reigning champion in the world of filters? Another question was what is the best all a round filter?
Do you want a reliably filtration for several years? (perhaps EHEIM)
Do you need a low budget filter?
Do you need an especially silent filter? (perhaps EHEIM)
Does is have to be able to take care of messy water by a big Pygocentrus shoal? (only big EHEIM canister like Pro III)
Is it only a great water circulation power you are after? (perhaps Fluval FX5)