Saffron is sold as whole threads or in powder form. Threads are preferable, since you can see what you're getting. Use your senses to examine the saffron: Look for long threads, about three-quarters of an inch, and a bright or deep red color, with few yellow styles. Smell the saffron, and taste it if possible. Pure dried saffron is very aromatic and tastes pleasingly bitter yet floral. A stigma placed on the tongue should never taste sweet. Ground saffron may be adulterated and often has less flavor.
Markets—even Indian ones—typically sell only Spanish saffron, both because of its quality and because it is widely available. The manager of one Indian market told me that he takes Spanish saffron back to India when he visits. Iranian saffron has been favorably compared with Spanish, but because of the trade embargo against Iran, it cannot be sold legally in the U.S. Nevertheless, it is openly available in Iranian markets in this country. It has shorter threads, and can have an excellent flavor. The best Iranian saffron comes from the Mashhad region. There is a saying in Iran that you must not eat too much saffron because it will make you laugh so hard that you could laugh yourself to death.