Below more detail about whats going to happen if you have multiple absorption shields which will be consumed without having a duration, so not like those flat duration absorbtion examples presented by you. So its a different thing, but just to let you know how those i mentioned will behave if they overlap in damage type.
I hope its not confusing.
If you still wondering which of the bubbles will get depleted first. I just did a test about this. Its always depleting the one with the shorter CD first. I am very certain about this. 3 skills with Aether absorbtion bubbles were used. Just standing next to a aether crystal was the method. 3 sec CD Crab was always first to be depleted, Ancrestral Ward as second with 16 sec CD, third from boots with 20 sec CD.