A have had both larger sizes and nano tanks. I choose nanos to buy and run now solely. I have gotten rid of all my larger tanks. Why?
A couple of reasons, some already stated; easier to scape, move, etc. However the main reason for me? It allows me to do different types of designs easier. You need less materials for the design, less plants and less time for a full carpet to develop. If you want to change your design, its much quicker to do so.
They can fit almost anywhere, at work, on a bookshelf... you dont need a large footspace to place the tank. In the same amount of space you have for a 55gallon, you can have... 4+ nano tanks.
Honestly though, it just depends on what you like, and what your goal is. My goal is mainly shrimp keeping... I dont need a large tank to do that, nor do I want to search a large tank when I'm breeding shrimp.
Its mainly just personal preference, I prefer nanos for the looks, size, and creative ability.
Not to mention the overall asethic designs of nano tanks. For example, my favorite nano I currently have is a Fluval Edge... its sleek and modern style fits what I like. The simplicity of an ADA tank or the Flora/EBI fits that too..