It used to be armor/resistance before block before absorb shields. Actually you used not to be able to block elemental damage at all back in the pre tbc days.
Now that Block is a percentage reduction it doesn't matter which way you turn it, so long as shields come last. 1x2x3 = 6, 3x2x1= 6 2x3x1 = 6 etc, doesn't matter which way you turn it around.
As for absorb shields, if I am not mistaken the biggest shield gets depleted first, then the second biggest, then the third biggest etc.