His best form came when he was our only striker. 15/16 he played down the middle and 19/20. He was hit and miss on the left.
He played most of 15/16 as a left winger, I'm pretty sure about that. We started the season with Rooney and Depay as striker options then drifted Depay to the left and kept Rooney as the lone striker, with Martial coming on he played the first few games as striker, but LVG found Depay so bad on the left so shifted Martial there and kept Rooney as the lone striker.
By second half of the season Rooney was shifted to midfield and Rashford became the main striker when he was promoted, Martial kept playing as left winger.
He was considered capable of playing both efficiently but he spent most of the season on the left due to Rooney and later on, Rashford being favored by LVG there, and because Depay was terrible with LVG on the left.