This answer is best answered based on personal preference as well as how smooth your walls are to start. The more shine the more attention will be drawn to the imperfections on the walls. Most popular options:
Flat: No shine at all. Perfect for low traffic areas like living rooms and bedrooms, as well as ceilings. Flat paint finish is popular now. However, if your walls are old this finish may be a bit unforgiving.
Eggshell: Has a tiny bit of shine and is a good choice for moderate traffic areas such as living rooms. This is by far the most popular option for most painters to use on interior walls. It will not show every imperfection on the wall as a flat paint finish may.
Semi-Gloss: Shiny but not glass-like. This is what you should use on cabinets and trim. Almost all trim is painted with semi-gloss.
High Gloss: Shiny! Used a lot for front doors. This is quite trendy now. It is being used on interior walls to give a modern and updated look. Can be very successfully used as an accent wall in a room.