The BMW F 800 S falls into the semi-sporty segment and the ST is a sporty tourer. Both models have earned their spurs. They share the same DNA, but the difference really lies in the seating position.
Both engines are extremely suitable for fine cornering, but you will still find a different type of rider on an F800S compared to an F800ST. Many accessories are interchangeable, but an ST is more likely to provide you with a complete set of luggage, whereas with the S you go faster for adapted brake and clutch levers or a different muffler.