This is how I understand the differences:
#1 This is a SimConnect variable you might be able to write to.
#2 Both are SimConnect events. The first is a toggle event you would use for a non latching push button. The other events can be used for latching (ON/OFF) switches.
#3 All are events. The first control the autopilot state directly, the second control the state of the panel switches which may have the same effect on the autopilot state.
Events and variables use different methods. Select the one that suits your use case.