Great post and helpful guide for people who aren't sure what the difference is between finishes.
What I usually tell my customers is that for most surfaces, such as walls and ceilings, flat paint tends to be more aesthetically pleasing than other finishes.
The reason why I believe that flat looks better than other finishes is that it softly reflects light. Any other finish will reflect light more sharply, especially with gradually higher sheens.
A common problem that people come across, though, is that most flat paint products don't hold up well on surfaces that get a lot of traffic. For this reason, satin or eggshell finishes are typically used, because inherently they hold up better.
But if aesthetics and durability are important to a customer, I will recommend a higher quality of paint. My go-to's are either Sherwin-Williams' Duration or Emerald. The benefit of those products is that every sheen is highly durable regardless if it's flat or not. Yes, they are a bit more costly than most other paints. But with those products, you're getting a high performance paint that will outlast most other paints.
For further information, you can find post on my blog about which are the best paint finishes for each room in your home.
http://huesandcoats.com/best-paint-finish-paint-sheen-guide/