Its true that chest freezers generally are more efficient because the cold air cannot flow out. On the other hand, how often will you open that fridge? A normal freezer in the kitchen is sometimes opened 10 times a day. How often will you take some film out? Once a day or even once every few days? I donīt think that it will make that much difference then. I would make the choice dependent on energy class and available space in your basement mainly. You should also mind that a freezer works most effectively when full, so filling the remaining space with food is a good idea.