The factory Motorcraft oil filter truly is a premium filter. It is made for Ford by Purolator and is essentually their PurOne premium filter innards with the conventional canister instead of the thicker PurOne can. That means that it has the synthetic paper filter media that is similar to the Mobil 1 and K&N and other premium filters. It also has the red silicon rubber anti drain back valve. Even if the other filters have slightly better media (which is doubtful) that would still make the Motorcraft FL-820S the best bang for the buck.
The K&N claims to have better flow charcteristics and if it is true that might be an advantage for hard driving.
Otherwise, the Motorcraft filter is every bit as good or better than all of the so called premium filters out there, including the PurOne, Mobil 1, Fram extra guard (the grey one), Fram (whatever they call the new on that comes in a sealed can and sells for about $10.00). I'll reserve judgement on the Amzoil filter because I'm not familiar with it. At least this is my $.02 worth.
