so ive been using synthetic since i bought my car. i love synthetic oil. its always been one over the counter though either mobil1, valvoline, penzoil platinum, once in a blue moon supertech full syn. how do you know whats the best out of them? i know products like royal,ams,schaeffers,lucas are better but like for what i listed they all claim to be the best? penzoil claims in ads to have destroyed mobil1 in tests? mobil1 has a huge positive track record and fan base. whos the best anyone know? and if it matters i prefer whatever will keep the engine cleanest.