I have a large-size upright freezer in the garage. I LOVE it. It is just like reaching in your home refrigerator, you never have to go digging down to pull out a heavy turkey, etc. There are shelves, and bins which slide out like drawers. I find an upright much easier to keep organized. The chest freezers are similar to a giant-sized picnic cooler, so ask yourself how often when you are at the park you have to pull everything out because what you want is at the very bottom. As far as size, it's not so much how many people are in the house, but how much food you want to store. If you have extra room, your food won't be crammed and you will have good air circulation which is necessary for proper freezing and maintenance of your investment. With extra room, you can also store some charcoal which will prevent odors. With extra room, you can store a few large blocks of ice at all times which you will need to prevent food spoilage during power outages, and which you can use in your large coolers in the summer time. With extra room, you can also store more food, which will help keep itself frozen longer during power outages (just like lots of big ice cubes last longer than just a couple small ones).
This is what my mother-in-law did her entire life, recommended to me, and what I have done for as long as I have been married. It works.
