After being in business for almost 10 years, this is still one of the questions I hear most.
There are pros and cons to everything, but this is my standard formula:
Moldings: semi-gloss or high-gloss. Why? That sheen is more durable and will wipe down easier when you are cleaning. Be careful of high-gloss, however. It is harder to touch up.
Walls: Satin or eggshell. Unless you want a room that looks like it has been lacquered. I’m secretly hoping that someone asks me to do this for them one day.
I rarely use flat paint. The only place it is acceptable is on the ceiling, but honestly, the ceiling gets ignored so much and there are much better options for it. We used high-gloss on our ceiling in our current house:
Do you want to save money or love all-white houses? Spray everything in a semi-gloss. It’s totally ok! Our painter charges extra every time he has to clean his equipment and switch colors (understandably). It also saves man hours to not have to cut in different colors. Go this route and you’ll save a hundreds dollars.
I hope this helps!