Activated carbon - My personal belief is that all brands are the same. Activated carbon removes impurities, smell and makes the water very clear but you need to change them every month. Again that depends on how much activated carbon you put into your tank and how much water & impurities there are in your tank. However, I don't think that activated carbon removes phosphates and nitrates.
Currently using activated carbon, Pura Complete and Pura Denitrate. Pura complete in my cannister filter & Pura Denitrate in my Skimz FR120. Henry from ML suggested this to me as he said that the Pura Denitrate will be most effective when used in a FR. But take note though, your flow rate must be really low otherwise everything will be blown out of your FR and into your tank/sump...