AT2 has more stability issues than AT3 does. With AT3 you can adjust the fulcrum to control the center of balance. Since the bandai stand adapter is so tall (the chunky but that actually touches the valk), banking the fighter on AT2 can cause the stand to bend.
AT1 is rock solid. AT2 needs user discretion to be solid. AT3 is not as solid as AT1, but is the most versatile out of the 3.