Written by Andy Fein, owner and luthier, Fein Violins:
Gut, Perlon, and Metal. These are the three basic materials used for making strings for violins, violas, and cellos. Each has distinct advantages and disadvantages. The best string is the one that works the best for you.
Natural gut, often referred to as "catgut", was the material of choice for strings for several centuries. Made from sheep intestines, not from a cat, these strings had the advantage of being from a material that was readily available.
In the early 1900s, string makers perfected the art of wrapping the gut core with a thin metal covering of silver, steel or aluminum. Gut strings give a very warm sound. Unfortunately, they are extremely susceptible to changes in temperature and humidity. They stretch and change constantly. For most players, gut strings are not a practical option.
In the post World War II years, artificial gut became available. They were named Nylon in the U.S. and Perlon in Germany. Soon after, string makers adopted these materials for use in violin family strings. The core of the string was manufactured with Nylon or Perlon and then wrapped with silver, aluminum, steel and other metals. These strings offer huge advantages over gut - they are far more stable than gut strings, last longer, have a clearer tone, and have much greater quality control. The early iterations of these strings had a tinny overtone. With decades of refinement, many brands of Nylon/Perlon core strings offer a refinement of sound very close to gut.
String manufacturers also experimented with using varying types of metal for the core of the strings. Alloys of steel and twisted strands of tungsten, steel, aluminum and alloys were wrapped in a variety of compatible metals. Success first came with all metal cello strings. Today, most cellists use one of the many brands of all metal strings. In recent years, very nice quality all metal strings became available for violins and violas as well. Well made metal strings are extremely stable, have excellent quality control, and have a soft feel under your fingers. Unfortunately, there are also several poorly made metal core strings on the market. Tinny, raspy and screechy would be the kindest descriptions I can come up with for these poorly made strings.
The type of string that will sound best for you and your instrument is dependent on your taste in sound and playability. My current favorites are:
Violins: Pirastro Obligato and D'Addario Helicore. Obligato strings (Perlon core strings) are great for higher quality instruments - they give the violin a very clear and warm sound with great projection. Helicore strings (the cores are constructed from twisted strands of various metals) work great for almost everyone else. They are very stable, soft under your fingers, last a long time, and have a wonderfully warm tone that carries far. These are my recommendations for A, D and G strings. E strings will require another blog.
Cellos: Larsen. The cores are constructed from solid cores of varying metals wrapped with silver, tungsten, aluminum and other metals. They sound and play great! They are warm, powerful, clear and have a fast response. Larsen seems to have the best quality control of any string manufacturer. Larsen cello strings consistently great strings.
These are my recommendations. The best way to pick the best strings for your instrument is to experiment. Put a brand on and play them for a month or two before you make any conclusion. The best strings are the ones that sound and play the best for you. No one plays with your bow arm but you. No one listens with your ears but you. Listen. Play. Make your own decision.