Which flash setting is the best for still photography?

It depends a lot on the lighting. If you are taking a photo inside, auto flash may be too much. Fill flash just fills in detail that would otherwise be hidden in shadow, that's probably your best bet. However if you're in a lot of light you might not want a flash at all.

As Perchik said, fill flash would be good if you're photographing things in bright sunlight and want to fill in the shadows.

Auto flash will generally give you good lighting, but it may look harsh. My favorite method, if you happen to have a tripod and some desk lamps or something, is to take a cardboard box and do this with it: http://strobist.blogspot.com/2006/07/how-to-diy-10-macro-photo-studio.html

The blog is primarily about off-camera lighting with flash, but if you make that box (cardboard box with the sides replaced with tissue paper or whatnot), you can then use the sides of the box to diffuse anything (sunlight, desk lamps, etc.), if you're not shooting in sunlight you'll need to do a pretty long exposure (with the flash off) and a tripod. You should use your camera's self-timer to keep it from shaking when it takes the picture, but you should be able to get pretty awesome looking shots for just about no cost.

bpeople has a very good suggestion, though if you don't have the energy to make the box, just lay a white sheet over a desk, so that there aren't any wrinkles, and point a couple lamps at it, and then use a tripod with NO flash (or if you don't have a tripod, i would recommend getting a chair, and using the timer feature as he suggested) - i've used this a lot, and it's a quick and easy way to make the photos look more professional.
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also, it would be worth it to look at your camera and see if there's a lighting function that you can adjust, under the menu, and then set it to tungsten lighting, if you're using regular house lamps to light the subject - it'll help your color not look quite as yellow.