140-160 degrees farenheit for most milk based drinks is what TASTES and FEELS best and even smells best. ANy hoter and it tastes nasty and burned and will burn your lips and it wil go tangy rather than sweet caramel.
My prefered temp is between 60 - 65 Degrees Celsius anything over it burns the natural sugars in the milk making it bitter. This is what i have been taught so i hope it helps.