Finding the best strings for a 12-string acoustic guitar depends upon a number of variables, such as playing style, the type of guitar and your own personal taste. All of the major guitar string manufacturers produce high-quality strings for the 12-string acoustic guitar. Ernie Ball, Martin, GHS, D'Addario, and D'Angelico all have strings to meet the your 12-string needs. Elixir is quickly becoming a major competitor among guitar string manufacturers, and they produce high-quality strings for the acoustic 12-string guitar as well.
The first thing to consider is what gauge strings to put on the guitar. Acoustic guitar strings are available in light gauge, medium gauge, heavy gauge, or a combination of heavy and medium strings. A general rule of thumb is that thicker strings produce more volume and tone. However, the heavier-gauge strings also put more stress and tension on the guitar neck, the guitar bridge and the guitar body. This is especially the case for a 12-string guitar. Take the condition, age and value of the guitar into consideration when selecting a string gauge. Also take the style of music into consideration as well.
Acoustic guitar strings are made from a steel core wound with bronze or phosphor bronze. Bronze and phosphor bronze are preferred by many acoustic guitarists because they produce a bright and clear tone. Phosphor bronze, made from a synthesis of copper and tin, has a slighter more mellow tone than bronze strings. A variety of bronze and phosphor bronze strings are available. Strings made by Ernie Ball, Martin, and GHS acoustic strings are among the most popular strings with 12-string acoustic guitar players.
If a mellower tone is more suitable to your 12-string guitar style, the bronze or phosphor bronze is not a good choice. A better choice is silk or steel strings. Silk or steel-wound strings produce a mellower tone that is similar to the nylon string tone on a classical guitar. D'Angelico 500 Silk and Steel Wound strings are good choices if you want a mellower tone for your 12-string guitar.
One problem with acoustic strings is that they lose their brightness relatively quickly and they have to be changed frequently. The reason for this is that dirt, grime, sweat and other contaminants build up on the string and penetrate the string windings. Elixir has created a solution to the problem by covering the strings with a special coating, the original poly-web coating and a newer nano-web coating. The coatings protect the strings against rust as well as contamination, ensuring the tone and longevity of the string. Poly-web-coated strings feel smoother than normal strings and produce a smoother mellow tone. Nano-web strings feel more like normal strings and produce a brighter tone similar to phosphor bronze strings. A set of Elixir strings for a 12-string guitar averages around £20 (as of April 2014), but they last three to five times as long as other strings.