Strings for an Acoustic Guitar

If you have an acoustic guitar then part of the fun is trying different strings to find out which sounds best and is easiest to play.  In 35 years of playing, I've tried every kind of string--and combination of strings--and am happy to share what I have learned with you.   Before thinking about strings, however, be sure your guitar is "set up" by a guitar craftsman, or luthier.  This means that the guitar has been adjusted to play easily.  Brand new guitars, even the expensive ones, require this.  It's extremely important.  A set-up generally costs around $50.00.
 
Gauges

      Guitar strings come in various gauges, or thicknesses.  a 56 gauge string is thicker than a 54 gauge string.  The most common gauges for an acoustic guiar are Extra-light (11-47), Light (12-54)  and medium (13-56).   (These are approximate listings - different manufacturers will vary the string gauges a little).  If you have a dreadnought guitar, I strongly recommend medium strings.  Why?  Because medium strings have a greater tension than Lights or Extra-Lights, and will transfer more sound to the top, or soundboard, of the guitar.  This is recommended for a new guitar, especially, because the top is tight and needs to be "played in."  However, medium gauge strings are harder to finger than Lights or Extra-Lights, but not by much. 
       Smaller guitars, such as parlor guitars, O, OO or OOO models will do well with Light gauge strings.  I do not recommend Extra-Light gauge strings:  they barely resonate on the soundboard.  Yes, they are easier to play but there will not be much tone coming forth from your instrument. 

Wrap-Wires

In most cases the strings you will use will have a steel core.  The bottom four strings will be "wound" with a wrap wire.   On acoustic strings, the wrap wires tend to be either phosphor bronze or 80/20 bronze (which is actually brass).   Phosphor bronze has a brighter, prettier tone, but is also slightly fuzzy.   80/20 bronze is initially brighter but then will mellow in a day or two.  Phosphor bronze will mellow also, but not quite as much.    Strings wound with pure nickel are generally used on electric guitars, but they will make an overly-bright guitar sound quite mellow and good.  Similarly, nickel-plated steel can sound very good on an acoustic guitar.  That is what Tony Rice uses, and he's a great guitarrist.   There are also strings which have an 85/15 formulation.  These strings are very mellow sounding and are good for an overly-bright guitar.   Last, Rohrbacher makes Titanium strings, wound with either phosphor bronze, nickel or coated bronze wire.  These strings will last longer than steel, since Titanium is non-corrosive.   They are costly (in the $20.00 per set range) but will last a year or more.   They have a slightly  softer, sweeter sound than  steel strings. 

Coated Strings

Virtually all string manufacturers  have a line of "coated" strings.  These strings have been either dipped or sprayed with a fine coating of  polymer that protects the string.  However, the coating  dampens the  sound of the string, and the guitar.   If your hands perspire a lot, then use coated strings, or the Rohrbacher Titaniums.   If your hands stay dry, then coated strings are not really necessary.  They cost a lot and really do not sound as good as uncoated strings.

Favorite Brands

D'Addario is the most famous brand and their strings are very good.   D'Addario also makes other brands such as John Pearse and Dean Markley (a not-very-well guarded industry secret).   Martin also makes a variety of strings and they are very good.   The Martin SPs strings are excellent and have a core of high-tensile steel.  This is a fine string for blues, or if you are bending the string.  DR Strings are hand made and are my favorite brand.   The DR Sunbeam phosphor bronze are extremely bright and good sounding; the Hi-Beam 80/20s are also top-notch.   GHS makes terrific strings also.  I would caution you about buying off-brand strings; they do not last very well.   If you stick with D'Addario, Martin, GHS  and DR, you will find great strings.   Rohrbacher Titanium strings  are patented, so they are the only ones who make them.  A British company, Newtone, makes hand made strings also.  They are expensive, fine strings, but I still prefer DR at the moment.  Sadowsky makes a wonderful pure nickel-wound string.  However, if you put pure nickel, or nickel-plated strings on your guitar, I strongly recommend a brass or bronze low E string:  the nickel doesn't sound good at that low pitch on an acoustic guitar.

In addition to eBay, there are many wonderful internet stores that sell guitar strings for a low cost.  Many have a flat rate of $4.00 for shipping - no matter how many sets you buy.  So, for under $20.00 you can sample a few sets of different strings and see what you, and your guitar, like the best.    Good luck!