Only main difference is the A2 outputs all it's audio formats to DTS where the A3 uses Dolby Digital so the audio has less bandwidth to work with which MIGHT affect sound quality on movies.
Other then that they should be close video quality wise though some claim the A2 drive is more forgiving of bad disks. I have a A2 and was happy to get it for the audio advantages it might have, never used a A3 so don't have direct feedback.