Guitar Strings
The first question is not which brand but which guitar: a classical takes nylon (Hannabach, Kingly Crown) and a folk or acoustic guitar takes steel (Earthwood), and steel tension on a classical top and bridge is enough to pull the instrument apart. Nylon trebles go false long before they break, so when the first or second string will no longer play in tune at the twelfth fret it is finished, and Kingly Crown sells the first, second and fourth singly, which means one dead string does not cost you a set. Steel strings are measured in hand sweat and practice hours rather than in weeks: once they feel rough under the fingers and leave dark powder on the fretboard, they are done.