The oven rack that is best for baking cookies is the middle rack. When the cookies are positioned in the center of the oven, they bake evenly.
If the baking sheet is placed closer to the bottom, the bottom of the cookies brown too quickly. The tops of the cookies brown too quickly if the baking sheet is positioned closer to the top of the oven. It's best to use one baking sheet for cookies and place it on the middle rack of the oven. If two baking sheets are needed, then switch the baking sheets around halfway through the cooking time. The positions of most oven racks are easily adjustable to easily move them where they are needed.