For a stand alone freezer, a chest type is of course preferable as it looses (spills?) less of the cold air when it is opened. It does require being perhaps a little organized. One can get racks/stands that fill the chest freezer in sections. One can then pull up a rack to raise the contents of that entire section.
As far as energy efficiency goes, I try to keep my current above-fridge freezer full.

If there's empty space I fill it up with 'freezer' packs (the blue gel things that stay frozen/cold for a long time). Doubly useful - I rarely have to buy ice for my cooler and every time I open the freezer and cold air spills out, there's less volume that needs recooling.