Gloss or semi-gloss, typically used on trim, reflects the light and will draw the eye to filled nail holes or overlapping trim. Matte or eggshell, on the other hand, have a more subtle sheen and absorb the light rather than reflect it. Read more about different lusters of paint here.
L// crown molding spliced together (not very successfully – my first attempt); patched with wood filler and sanded.
R// the same crown molding caulked and painted with matte finish paint.