The bulbs used depends very much on what the designer of the fixture had in mind. Those intended primarily for decorative lighting will/ could utilize lower wattage incandescent bulbs.

Low voltage mr16 lights could also be used in other cases to provide small bright spots.

If the requirement is for task lighting, the items that matter the most are
1. Amount of light output - lumens, candela, ...
2. Spread of light.
3. Light temperature 2700k for warm yellowish light
4. Color rendition.

The choice of bulbs is affected by factors such as
1. the base of the bulb for example e26 base, bi pin, etc.
2. Low or line voltage
3. Dimming controls- most cfls are automatically ruled out by default.
4. Form dictated by the fixture.
5. Local energy efficiency mandates.

The most common base is the e26 and will continue for quite a while.