What is Fish tank 3 stage filtration?

There are so very many to choose from that it is impossible to compare them all. I would advise you to go for an external power filter that has several types of media that can be cleaned at different times without damageing the Bacterial content of the media too much. I do have one warning though. Never ever use an "Undergravel Filter" they are likely to release deadly toxins into your tank if you ever have a power blackout and kill all your fish.