Today there more kinds of strings than there were 40 years ago, a dozen or so synthetic-core strings, a multitude of steel-core strings and still some gut core strings. Most of these strings have been introduced in the last few years. The major string manufacturers are constantly introducing new products, which can be overwhelming and confusing for musicians. But a little knowledge will help you through the string-buying maze.

Keep in mind that there is no single perfect string for everyone. The trick is to find a string that complements the qualities of your instrument and your playing style. Below you will find a guide to the basic qualities of each type of string—gut, synthetic, and steel.  Some sets are available with alternate winding options on certain strings. 

GUT-CORE STRINGS

Musical-instrument strings have been made of sheep or lamb intestine since the earliest days. Until the end of the 19th century, gut strings were the only strings available. On the violin, the E, A, and D strings were usually plain unwrapped gut. The G string has taken different forms to reduce mass, using forms of twisting, braiding, and wrapping. Today, musicians specializing in early-music performance are among the few using plain gut strings. Most who use gut-core strings use those that are wrapped with silver or aluminum.

Gut-core strings have their own unique sound, which is very full and complex with lots of overtones. Of all types, these strings have the slowest response. On many instruments there is a slight resistance, or "catch," on note or bowing changes, an effect that is more pronounced on some instruments than others. Because they are lower in tension, gut strings tend to feel softer and more pliable under the finger. On very good instruments gut strings can pull a sound unlike any others, with unique overtones. 

The major disadvantage is that they are rather unstable in response to temperature and humidity changes and thus tend to go out of tune frequently. When first installed, gut-core strings need about a week to stretch out before they have any kind of stability at all. Some musicians get tired of the constant tuning. The sound of these strings, however, can be beautiful, and although manufacturers of synthetic-core strings often claim their strings sound just like gut, they usually don’t quite make it. Gut core strings tend to make the best instruments sound even better, but on lower priced instruments they can be a detriment. I don't generally like them in humid climates as they tend to sound like rubber bands.

SYNTHETIC-CORE STRINGS

In the early 1970s, Thomastik-Infeld revolutionized violin-string making by introducing Dominant perlon-core strings. The claim was that now you could have a string that sounded like a gut-core string but didn’t have the disadvantages of pitch instability and slow response. These strings use a core of perlon (a type of nylon) wrapped with silver or aluminum. Within a day or two of installing the strings, they stretch out and stabilize. The core isn’t affected by changes in temperature and humidity nearly as much as gut, so these strings stay in tune much better. They also have a quicker response. Since the introduction of Dominant strings, other manufacturers have introduced many new synthetic-core strings using not only perlon, but also high-tech composites such as Kevlar. Each string has its own particular sound quality.

Until Pirastro introduced its Tonica strings, the company seemed to be having trouble competing with Dominants. Tonicas are excellent strings with a bright sound. The sound is not as bright as that of the Dominant, but it has more complexity, fullness, and depth. Some people may find the string to have a slightly slower response. Two E strings are available, one plain steel and one with aluminum wrapping. I’ve found the wrapped E to be very useful on violins that have a tendency to squeak when going to the open E.          I feel that these actually give a nice darker sound compared to Dominants and tend to be closer to a gut string sound.

When Pirastro introduced the Obligato, I found it to be one of the more interesting strings on the market. Of all the synthetic-core strings, the Obligato comes the closest to sounding like a gut-core string, namely the Eudoxa. Obligatos are, however, more responsive and slightly more brilliant. If you have a violin that would work well with Eudoxas, you might want to try the Obligatos. I would also suggest them for overly bright instruments. The standard set includes a silver-wrapped D and a gold-plated E.  Strong Warm Gut-like sound

STEEL-CORE STRINGS

Steel strings began to appear in the late 19th century with the introduction of the steel E string (most E strings still employ steel in their creation). The A, D, and G strings use a core of fine strands of steel covered with a variety of metals, including chrome steel, silver, tungsten, titanium, and others.

Many (but not all) steel-core strings have a tendency toward brightness. The sound is usually clear but simple, with few overtones. Steel-core strings have the fastest response of any string. Most are higher in tension and thinner than other types of strings. The least expensive of them tend to be edgy, tinny, and a bit rough. The best are of a much higher quality.

With steel cores, there is very little expansion or contraction during temperature and humidity changes, and they tend to stay in tune better than synthetic-core strings. They are therefore a good choice for beginning students.

I prefer the Piranitos for a similar price