Synthetic oil is generally better than conventional oil or blends because it lasts longer and may improve the car's performance. However, it is also usually significantly more expensive.
Some cars require synthetic oil, so owners should always check their car manufacturer's recommendations before deciding which type of oil to use. These owners should also carefully read the labels of oil before use, as some blends appear to be full synthetics at first glance.
Although older synthetic oil formulas had a tendency to leak, modern synthetics are more efficient than conventional oil and can last for up to 20,000 miles without needing a change. They also perform better, especially at extreme temperatures. The engine's better performance can also slightly increase its fuel efficiency, saving the driver money on gas. Blended oils can also provide some of these benefits when compared to full conventional oil, but the difference is usually significantly smaller.
Synthetic oil is also better for the environment than conventional oil or blends. The chemicals used to make it are hazardous and it still needs to be recycled properly after being changed, but less frequent oil changes mean less oil is used overall. Depending on the vehicle and owner, these less frequent changes can also balance out the higher cost of pure synthetic oil.