Kate, Looks like with all the different kinds of sedum offered so far, it will come down to what color did you have in mind to go with the surroundings (especially the color of your pot; not all terra cotta is the same shade). And the color may differ in contrast to what semps or other plants are around it. Some apple greens may not look quite right with the blue greens.
Don't forget about texture...which can be just as important as color.
Lastly, I, myself, worry about the ease in which each sedum candidate would grow. I saw Lynn's suggestion of Ogon and it brought a smile to my face but I couldn't keep it alive to save my life...so I tend to choose what is easier to grow.
Good Luck!
