(Updated 12/19/19)

I get questions from folks regarding strings for instruments, what brands I prefer, what type strings, how often do I change them, clean them, etc.

Regarding brands and gauges, my first answer is usually this.  "It's a matter of personal preference.  Everyone has their own take on strings, and how they sound.  No doubt, everyone hears things a bit differently.

However, I've done a lot of experimenting over the years, and as a general rule, these are my preferences for acoustic instruments:

1.  D'Addario guitar strings.  They are consistently at the top of the heap for tone, quality, price and sound.  They vacuum seal their strings, so you can buy them and store them, and still have confidence they have not degraded when sitting in your closet.  I remember one Christmas, I bought several cases of high quality strings marketed by a prominent guitar manufacturer.  The first couple sets were terrific.  The strings were in paper envelopes, and not vacuum sealed.  By next year's end, I had several dozen sets of strings which were showing signs of corrosion and deterioration, presumably caused by variations in humidity and temperature while in storage.  That won't happen with D'Addario strings. Taking their lead, other manufacturers are vacuum sealing their offerings.  Remember, strings have a shelf life, if they're not properly sealed or otherwise protected, they will deteriorate.  'Nuff said about that.

2.  I use Phosphor Bronze strings exclusively.  This a matter of personal preference, others may chose differently for good reasons of their own.  I find their tonal range superior, with a bit more heft on the bass side.  They are also more durable. 

3.  I use medium strings on my Martin D-28, and on my Larrivée LV-19.  Those instruments are built to handle the tension and the medium weight gives them a lot of sound projection without loss of clarity.

4.  I sometimes use mediums on my lighter guitars (Martin 000-28 size instruments).  Medium string tension can take those instruments right up to the point where they're being stressed.  Having said that, I've had no issues with any adverse impact on the instruments.  On a high quality instrument like a Martin 000-28EC or comparable, I now tend to go with light gauge strings.  Here's why.  The lighter gauge loses a bit in volume and projection, but picks up more than it loses in tonal clarity.  A high quality guitar build will, on its own merits, give better sound volume and projection, so on something like the 000-28EC model, you'll notice the increase in quality of tone, but will hardly notice any reduction in volume.  I've spoken to top players about this, and they agree.  Pat Donahue, for example, uses lights.

5.  Now, if you don't believe the above, or can't live without volume on your non-dreadnaught instrument, then you might want to check out light-medium strings (heavier gauges on the bottom three strings, lighter gauges on the top three).  I used them for several years and they were fine, except in the end, I didn't feel I was getting enough punch out of the G, B and E strings.  The combined tension on these is less than mediums.  More recently, on my orchestra size guitars, I've been consistently using D’Addario "True Mediums."  These give the same bottom and top gauges that you get with mediums, but are lighter gauges in between.  The combined tension on this package falls closer to lights than to mediums, so they're a very good choice as a solid compromise on the issues of tension, projection and tonal qualities.  Only downside is they're a bit more expensive.

6.  "Billy's Secret String Treatment"

If you play a lot, you'll change strings frequently, think every 50-75 hours as a minimum.  The main problem is strings deteriorate if you're not careful how you use them.  For example, are you washing your hands before you play?  Do you wipe them down when you're done?  Do you treat them with anything?  Keeping them clean is the most important thing.  Casual wiping with a cloth is OK, but usually not enough.  In the old days, we used to mix up a batch of WD-40 and rubbing alcohol, split 50/50 and cleaned/lubed the strings periodically.  It made a difference.  Strings maintained their playability, tone and projection with minimal notable loss over time.  What would que me to change the strings would be my seeing fret indentations on the bottom of strings.  When indentations become visible to the naked eye, it's time to change, even if they still sound good.  It's no fun having strings break during a performance.  Abiding by this rule will spare you the pain.

Always experimenting, I eventually came upon the following method for ensuring longevity and on going performance quality of my strings.  Here's the deal:

Ingredients:

1.  Dr. Duck's Ax Wax and String Lube (buy online or at your favorite retailer; about $12/bottle.  One bottle will last several years)
2.  Gun wipes (aka bore cleaning pads); no less than 2" square, a little larger if available.
3.  A small container with a twist on cap (usually an old plastic cosmetic container will work).

Formula:

1.  Fill the container with pads (usually 15-25 for me)
2.  Squeeze the Ax Wax directly on top of the pads, until enough is released to ensure the liquid spreads to the pads while they remain stored in the container.  This doesn't take much ... the fluid is viscous and spreads well.  To ensure even spread, every once in a while, turn the container over. 
3.  Just let it sit until you need it.

Application:

Every week, I take one pad out to use.  Before I play any stringed instrument, or before gigs, I take the pad and wipe down each string.  I do this by cradling the string with the pad, then twisting the pad tight, afterwhich I slide it the length of the string (both ways, several times).  Of course, on mandolins, I do two strings at a time.

After I wipe down the strings, I do not discard the pad ... I simply let it sit on top of the container.  Each pad will give service for about 1 week.  After that, then I discard, and replace with fresh.

This process keeps strings clean and sounding fresh with clear dynamics.  You'll easily triple the play life of whatever string you use.

Dr. Duck's Ax Wax works best, I've tried them all.  As I said earlier, before Dr. Duck's, I mixed WD-40 with rubbing alcohol, half and half; but I no longer do that.

I never use coated strings.  Don't like their dynamics.  This process is recommended for normal strings.

Hope this helps,

Billy