I had the same dilemma. I recently added insulation to my attic after the ductwork. It was a blown in insulation. The issue depends on what insulation you are using. A bat insulation seems like it would be better before you put in the duct work. I had my blown insulation put in after the ducts because it would seem to me that someone crawling and putting in the ducts would make a mess of the blown insulation. Check with your contractors. Just my two cents! Kudos to you for adding insulation to your home!
The Carrabba Group
Keller Wiliams Hollywood Hills