Is it better to turn it off or leave the car running when taking a coffee brake for 5-10 min?

 

If the car is warmed up, and you are not doing this multiple times, it is definetly better to stop the car. If the engine is not warmed up, or you need to make start and stop your car multiple times in a short period of time, it would be better to let it idle.

You should NEVER EVER let your engine idle for 5-10 minutes. You are definetly wasting a lot of fuel, not burning as clean, fouling the combustion chamber more, and making your car easier to steal.