Q:

In actionscript, if multiple instances are listening for the same event, which executes first?

I have various instances of various classes all listening for ENTER_FRAME. I need to know what order they will execute in.

A:

By default event listeners are executed based upon the order in which they were added:

Event listeners with the same priority are executed in the order that they were added, so the earlier a listener is added, the sooner it will be executed.

But you can control this order by the priority param:

When you call addEventListener(), you can set the priority for that event listener by passing an integer value as the priority parameter. The default value is 0, but you can set it to negative or positive integer values. The higher the number, the sooner that event listener will be executed. 

Ref: http://help.adobe.com/en_US/ActionScript/3.0_ProgrammingAS3/WS5b3ccc516d4fbf351e63e3d118a9b90204-7e54.html
Beware that with broadcast events, i.e. ones attached to multiple objects, the priority param does NOT effect the event order across multiple objects, only the order within listeners attached to the same object, thus the execution order is still controlled by the order in which they were add.

