Aside from the color and design, I also take into consideration the thread count, the quality, construction and the finishing.
Thread count usually range from 80 to 1000 (to 1020). The higher the thread count, the softer the fabric feels.
The quality of yarn used in the fabric also affects the quality. I have read that the world's finest cotton is the Egyptian Cotton.
Italy is known world-wide to have the finest spinners, weavers and embroiderers. Try looking for linens made in Italy and compare it with other linens and see if you are able to spot the difference.
Most made-in-Italy cotton sheets are mercerized. It is a process where the fabric is treated with sodium hydroxide to shrink the fiber and increase its luster and affinity for dye. The finishing brirngs out the subtle sheen of the sateen, the softest nap of cotton, the richest long-lasting color and enhances both the feel and quality of the fabric.
One of the best and renowned manufacturers of luxury and the finest linens is Sferra. An institution in fine linens, it offers the best in Italian linens. It also offers 1020 thread count and 100% Egyptian cotton sheets. Known for excellence in quality and design, Sferra has provided furnishing for heads of state and even the Vatican.