I used to research this stuff to death, mainly just staring at graphs and oil tests etc.... Yes every oil company will claim they are the best. When is the last time you heard a company say "Our oil is almost the best." But from what I have read, Amsoil is the way to go. Royal purple is probably next however Amsoil did some comparissons And recommend you change it more often because it contains Moly-b which is anti sieze compound. Works great but apprently can clog filters, and passages when run for extended periods, but were talking over 10,000 miles. My big complaint with Amsoil is local availability, I have to order it, in fact I ordered a case last week and have yet to hear from anyone about it. Price is not an issue with me bacause it basically pays for itself in regards to longevity, Amsoil invites the customer to do an acidity test on there engine oil, and you will find it maintains like new levels and then some under most conditions and using there heavy duty filter.

In a nutshell, from what I have read in the various forums, tech data etc....Amsoil is the way to go, however it is the filtration method used that matters most. If you use there bypass oil system you can run the same oil for a VERY long time. I just use the Heavy duty Amsoil filter, its over twice the size of stock and filters some thing like .5 micron.  The bypass setup can cost about 180 bucks. There is a writeup on it on 4x4wire.com

http://www.4x4wire.com/toyota/tech/amsoil_bypass_filter/