The larger one is great - as it has weighted feet. This is our preference, as the more compact one requires double sided tape to affix to the desk, making it less mobile. Both are highly adjustable in height and angle.

The 18-inch size is the most versatile and meets most of my needs. I liked the weighted feet better than these non-weighted feet, but this style takes up much less room on the desk and is easier to set up initially.