In clothing sizes, a 1X refers to the smallest size in plus women's clothing, while XL refers to a larger size available in normal women's clothing. Sizing for clothing varies by brand.
1X is considered a larger size than XL as it is part of the plus women's sizing charts. Sizing for clothing items are extremely inconsistent and often vary based on brand and material that you are purchasing.
The best way to know if someone should be wearing a 1X or XL clothing item is to try on the two sizes and see what fits best. In doing so, the person can guarantee that they purchase the item that has the best fit.