In the early days of the guitar family, strings were made of real animal gut. It was a matter of necessity: that was the best thing they had to work with at the time. Thankfully, science has given us better alternatives over the years. Nylon strings replaced gut strings on classical guitars decades ago, offering the same traditional character in their tone with none of the disadvantages of the old strings. In fact, nylon strings themselves have further evolved since they were first introduced. Today, you can get nylon strings in lots of different varieties. Each style produces its own distinctive sound, which means that personalizing the voice of your guitar can be as simple as swapping out its strings for a new set.
Choosing the best nylon strings for your classical guitar will come down to a few factors. One of the most important is scale: after all, the strings won't be much use if they don't even fit on the instrument! For a 1/2 size guitar, check out some top-selling sets like D'Addario's EJ27 Nylon Classical Guitar Strings. Interested in a full-sized set from the same series? Take a look at the EJ27H Classical Hard Tension Guitar Strings. Want an identical-to-stock replacement set for a Martin guitar? Maybe the Martin M260 80/20 Bronze Ball-End Regular Tension Nylon Classic Guitar Strings will fit the bill.
Although nylon strings are considered traditional, that's not to say there aren't some more exotic options to choose from if you'd like something special. For example, there are sets like the RC Strings CNL40 JG Carbon + Nylon High Tension Nylon Guitar Strings, with carbon-treated windings for a unique feel and longer string life. If you'd like to try out A-tuning on a Cordoba Mini, then you'll appreciate the Cordoba 05279 A-Tuning Mini Ball-End Nylon Acoustic Guitar Strings. And these are just two examples of the specialty strings you can find in this section.
So how classic do you like your nylon strings? Whether the answer is strictly traditional, or modern and purpose-built, there ought to be a few sets here that will provide exactly what you're looking for. In fact, you might even decide to try out a few different varieties, and that's a great idea - experimentation is the best way to figure out what sort of nylon strings will deliver the perfect tone to suit your musical style and personal tastes.