Wow, this is awesome - an oil filter war! I'm not aware we've ever had one before!
I am of the crowd that believes the best you can get is the Fleetguard Stratopore.
As far as Amsoil and Donaldson having higher micron ratings, isn't it true that with a fixed volume filter the flow rate necessarily decreases with decreasing minimum particle filtration size?
If that's correct, then we must ask whether the improvement in particle filtration is worth the drop in overall oil flow rate.
Particle size is not the only measure of filtration effectiveness - it must always be balanced by a flow rate matched to the system demand. I can make an oil filter that filters to 0. 001 micron absolute, but to fit it into a canister for a Cummins B-series it wouldn't flow enough oil.
Don't get me wrong - I'm not bashing Amsoil or Donaldson. They're not stupid, so they must have considered these things in their filter design. So perhaps the question is, why did each company make the choices they did?
Ryan