Sapphires have been popular for ages. Part of it's popularity is due to beautiful color. Sapphires are most often found in a deep blue color but can come in other colors, like pink, yellow, or white.
It is also a popular stone because of it's strength. It is a 9 on the Mohs hardness scale, which is only one below a diamond, so it's a resilient stone that is easy to take care of.
Lapis is another gemstone that is used as a birthstone for September. Often Lapis have gold veins or flecks in the blue color. Most often they are found in Afghanistan and ancient Greeks and Romans highly valued Lapis stones because of the beautiful color.
Either of the stones for September are memorable choices. They bring such beautiful, rich color to whatever they are paired with. I love the pink sapphires and the gold that is in the Lapis. Do you have a preference?