My opinion would be that the saute pan would be the most versitle for me, but since I don't know what or how you cook I can't say which would be best for you. But, here are some things to think about:
The 12" saute pan is deeper than the fry pan, has straight sides, so the bottom (cooking surface) is going to be nearly the diameter of the top of the pan (about 11.75" probably). To me, this is the most versitle. - there is nothing I couldn't do in it if I had only one pot/pan.
The 12" fry pan is not as deep and, bacause of it's sloping sides, has a smaller diameter bottom (9.25") - so it has less "cooking surface" than the saute pan. If I only had one pot/pan - this would be my second choice.
The 12" chef's pan is somewhere between a small Wok and a large Saucier. It would be the most limited of use, to me, since it has the smallest cooking surface - only about 6".