This one:
The primary cause of the accident was that the crew attempted an improvised test of the AOA warning system, not knowing that it was not functioning properly due to the inoperative sensors. They also disregarded the proper speed limits for the tests they were performing, resulting in a stall.

The aircraft's computers received conflicting information from the three angle of attack sensors. The aircraft computer system’s programming logic had been designed to reject one sensor value if it deviated significantly from the other two sensor values. In this specific case, this programming logic led to the rejection of the correct value from the one operative angle of attack sensor, and to the acceptance of the two consistent, but wrong, values from the two inoperative angle of attack sensors. This resulted in the system's stall protection functions responding incorrectly to the stall, making the situation worse, instead of better. In addition, the pilots also failed to recover from an aerodynamic stall in a manual mode in which the stabilizer had to be set to an up position to trim the aircraft. But only the stick was applied forward, the aircraft did not trim itself because it was switched to full manual mode. Seconds later the plane crashed into the sea. See any similarity between Max and Bus accidents.....one high and one low speed but both had elevator and stabilizer at settings that were opposite to each other, and only a jackass does a dirty stall series at 3,000’!