Phosphor Bronze guitar strings are widely considered to be the best choice for acoustic Guitar, providing a warm, pure tone.
Elixir's Nanoweb Phosphor Bronze strings are a fine example of this.
The Nanoweb coating prevents dirt and dead skin cells from building up in the grooves between the winding on the strings which allows them to last 3-4 times longer. In addition to this, the coating makes the strings smoother, improving playability and reducing finger squeak when changing fret.