You have the choice of four basic finishes when it comes to painting the trim in your home. Flat (matte) paints are just that, flat. They have no shine, and are the most delicate of paints, unable to stand up to much scrubbing or other abuse. Eggshell or satin finishes are slightly harder and shinier than flat ones. Semi-gloss is more durable than the first two, without the super-high gloss of your final choice, which is glossy finish. Glossy finish is enamel-like and cleans up easily, but is difficult to use, as it does not hide mistakes in application or flaws in the surface as flat-finish paints can.
When it comes to painting trim, most people choose either a semi-gloss or high-gloss paint. These choices play well off flat or satin-finish walls, causing the trim to stand out and act as an accent in the room. Glossy paints clean well, so are ideal for high-traffic areas like doorways. The gloss also serves to accent the detail in the woodwork, causing it to stand out that much more.
There are a few drawbacks to high-gloss versus semi-gloss paints for trim work. High-gloss does bring out flaws in the trim, so if you are repainting old trim that may have some defects, semi-gloss may not show them up quite as much. High-gloss paint is the most difficult to touch up, as such areas do not blend well into older paint. Finally, application of high-gloss paint takes a more expert touch to achieve a seamless and flowing result; high-gloss paint is extremely unforgiving.
As a rule of thumb for repainting your home, flat or satin finish is chosen for ceilings and walls, with trim work being one step glossier than the walls. So for flat walls, do a satin trim, for satin walls, use a semi-gloss finish. Kitchens and bathrooms do well painted entirely in semi-gloss for easy cleaning. Small rooms like bathrooms can utilize semi-gloss throughout, including the ceiling.