Which modulation method will result in the highest theoretical data rates?

According to the Wi-Fi - Radio Modulation - TutorialsPoint document1, 64 QAM is a modulation method that will result in the highest theoretical data rates among the given options. 64 QAM uses both phase and amplitude modulation to encode six bits of information into each transmitted symbol. It can achieve up to 54 Mbps in the 802.11a and g systems.

References: https://www.tutorialspoint.com/wi-fi/wifi_radio_modulation.htm