"You can utilize the height better with something like a moss wall, or maybe some tall rocks or driftwood. "
Absolutely. Look, let's face it, if you have extra cash to spend, get the larger footprint in the 12L It looks great and allows more "elbow room" when walking. Plus, when planted, it's a real conversation piece!
However, 99% of the time I use tenners. Why? Cheap, and I can fit more tanks in the same space as a 12L takes up. My shrimp enjoy hanging out on the sponge filters and moss. Moss itself is a jungle gym with food and provides a really nice area for a shrimp "coffee lounge." Plus, it helps keep the shrimp contained for quick breeding when a fem molts.
As said though, the footprint of a 12L just cannot be beat!