There are a few key differences. First, a chest freezer has more depth, so it uses baskets that allow you more storage options without digging. The downside is that you can’t reach items as easily from the top because they’re buried in all that space – which also means those items are harder to find.
Chest freezers tend to be cheaper to maintain than upright units as they are more efficient.
Don’t forget that some upright freezers have an ice-making function which chest freezers do not.