Funny you should ask! It is my opion that synthetics are best. Out of the synthetics the higher the concentrations of TMP and TPE the better! It is my opion that by reduceing carbon, ash, varnish and sludge deposits the seals, ring pack, egr valve and guides will live a long and happy life.
I am sure that additives like Lube Control, Auto-Rx and Nuetr 131 all help as well. I would rather have an oil that does not generate alot of waste to deal with!!