D'Addario EJ16 Phosphor Bronze Light Acoustic Guitar Strings, Single

 Warm, natural, lasting tone
I have used D'Addario EJ16 for about 10 years now and have occasionally tried other popular brands and newer formulas (coating, etc.). I may be just stuck in old school because I've been playing about 25 years, but I like these precisely made traditional steel strings for acoustic steel sounds better than any others I've tried.

EJ16's get in tune and stay in tune quickly within minutes of being newly strung. The tone remains crisp for several days after being strung and then transitions to a less crisp, but still distinct warm sound. I'm festidious about tuning so I also love EJ16's because they usually only need a touch up even using a Peterson tuner. The gauge sizes on this set are also big enough to really activate the soundboard of a nice (or any) acoustic, but they're still light enough to be pleasant to play and can be bent for vibrato. I'm guilty of not changing strings as often as I probably should, but they will stay in this middle state of a nice sound for at least another 2 to 3 weeks. Giving them a vigourous cleaning will eek a little more life out of them. They'll eventually get dull sounding and not tune up as precisely after plenty of use/time (usually about a month for me playing at church and other places multiple times per week).

I use D'Addario for classical acoustic, rock/pop electric, 12 string acoustic and jazz electric. I've tried many other brands but I beleive they simply know more and have invested more than anyone else in making strings for all sort of instruments. They have some newer formulations such as web coatings, but I think the pure, natural sound and crisp tuning of the EJ16 is better (and more cost effective) for the music I play.