The 'critical' Engine is the one on the upwind side, i.e. on the side which the wind is coming from.
Reason is that is wind is pushing against the horizontal fin and thus pushing the airplanes nose 'into' the wind. If the wind is coming from the port side and the No.1 Engine fails, the starbord engine is going to push the airplanes nose even more to the left, so this is the quickes way you encounter control problems.
Regards MAX