Royal Purple SAE 5W-30, Mobil 1 Extended Performance, and Pennzoil Ultra Platinum are highly-rated full synthetic motor oils. These are the top-rated brands by Injector Cleaner Boss.
Synthetic motor oil is specifically formulated to lubricate engine parts for longer and flow better than conventional motor oils at cold temperatures. Synthetic oils allow for longer periods of time between oil changes and reduce wear and tear on the engine, resulting in longer engine life. Because of their highly advanced formulation, synthetic oils cost more than conventional motor oils.
As of 2015, most vehicles do not require the use of full synthetic motor oils. Newer models of high-end brands such as BMW, Audi and Cadillac do require full synthetic motor oil. Check your vehicle's owner manual to determine the right type of oil for your vehicle.