The marking style mostly depends on your pressing style, which in turn depends on your playstyle. Usually, attacking formations should press high, and it takes up a lot of condition. Since it's expected that the ball will be in the other half, you should not need sophisticated defending, so use zonal marking to save energy. I don't even press high against way weak teams (I don't play attacking, but as they say, attack is the best defence). I play defensive counter attacking, so it's important to win the ball back IN YOUR OWN HALF. So it's essential to press low in this case. With man-to-man marking, the opponent are more prone to giving it away, thus a counterattack can be executed. Man marking can also be effective if want to drive a bus
Man marking can be extremely effective, but for that your defensive players should have good positioning and marking skills.