Wife and I designed the floorplan for our home, and the developer then wrapped a shell around it that matched the other homes in the neighborhood. We worried a lot about the placement of windows, the number and location of electrical outlets (the sales person thought I was going overboard, but we don't need extension cords - anywhere), the view of the fireplace when you walk through the front door, etc.. We thought through every detail - - -
But we overlooked specifying that there should be access to the attic crawlspace. Oops!
Several years later, we changed out the lighting in the kitchen, and the electrician needed to access the crawlspace. So he ended up cutting an opening in the garage ceiling. Naturally, his position was that he was fine with cutting openings, but someone else had to do the patch later. I looked into the possibility of putting pull-down stairs in the opening - the garage ceiling is 10', and Home Despot carries pull-down ladders that can handle that height. But the problem that I ran into was that local building codes require that the garage have a sealed envelope - the concern is that carbon monoxide from cars in the garage could seep through unsealed opening and get into the house. So all we could do was seal the opening with sheet rock.
But to answer the question - my choice would be wood. Aluminum is fine for extension ladders that need to be light enough that they can be schlepped around the house, but if the aluminum is damaged, they are dangerous. Wood is heavier and less subject to damage. And for a permanently-installed pull-down, weight isn't relevant.