Every musician who plays a fretted instrument needs to choose their strings wisely. The reason is because some strings are more suitable for certain playing styles and genres than for others. Today's line of strings for fretted instruments is considerably large - in fact leading string brands specialize in a wide range of electric guitar strings acoustic guitar strings classical guitar strings bass guitar strings ukulele strings mandolin strings and banjo strings. These brands include Elixir D'Addario DR Ernie Ball Martin Fender and GHS.
The biggest impact on the playability and sound of a fretted instrument is the thickness (or "gauge") of each string. Lighter gauge string sets are usually preferred by beginners because they are a lot easier to hold down and notes are easier to bend. However as a player progresses they can think about moving up to a thicker heavier gauge. Thicker gauge sets require more finger pressure to fret and bend but they also produce more volume and sustain which is why (at least when it comes to electric guitarists) they're favored by metal and hard rock musicians.
Another factor to consider is the material used in the making of the string. For electric guitars and acoustic guitars two common materials are nickel-plated steel (known for its bright attack and balanced warmth) and stainless steel (used often for acoustic guitars - typically associated with folk and country music). Some strings are even polymer-coated to add to their durability. As for classical guitars they're fitted with nylon strings to suit the soft mellow tone that's needed to play flamenco and folk. Various string windings are also used the two most common being roundwound (which offers a bright aggressive tone that's ideal for rock) and flatwound (which produces a smooth dark sound that's perfect for jazz and blues). Bass strings are also available in both flatwound and roundwound string windings.
Quality strings mean quality sound - this can be said for any fretted instrument and with a little time and effort anyone who has a specific tone in mind should be able to find a string set to match their tastes skill level and playing style.