Assuming you are talking about a 2.0L turbocharged engine in a passenger car, the best gas to use is premium unleaded gasoline with an octane rating of 91 or higher. Turbocharged engines are designed to run on high-octane fuel in order to prevent knocking and pre-ignition, which can cause serious engine damage.
If your vehicle's owner's manual recommends using premium fuel, then that is what you should use. If the manual says that regular unleaded gasoline is fine, then you can save some money by using that instead. However, if your car is experiencing knocking or pingi