Aluminum is softer than steel and reacts differently when working it. Just because it is softer, don't think it is easyer to get it to where you want it. I prefer to work steel, for steel does not spring back as much as aluminum.
You could hammer it yourself, but you could also run the risk of splitting the aluminum or hitting it so much that it gets thin and wants to oil-can. Then when a body shop gets involved to finish the shape, they may have problems.
I would seek a good body shop that has experience with working Aluminum. Size does mater, as does location and complexity of repair.
Body shops use me to do PDR. Wanna see what they ask me to do? Here is the before photo. Next post you'll see the refection of the husban/wife in the door. They'd have a bigger smile if it was a Healey!