The nylon string acoustic guitar has a softer, mellower sound than the steel string guitar. Strangely, modern audiences can still be spellbound by the depth of feeling of a nylon string guitar. It’s entirely up to you which one you choose to play. I could cite a list of artists who used either nylon or steel string for this or that record, and make a wild guess or two at why the artists made the choices they did, but the bottom line is that if you want a deep, quiet sound that doesn’t compete with your singing, the nylon string guitar is the way to go.
When you go out to buy a guitar, go past the general music store and on to your local guitar dealer if you have one. That way you will have a guitar expert guiding you and not some dufus who only plays two-and-a-half chords. Don’t let the guy in the store automatically steer you to the top-of-the-range guitars, and equally don’t succumb to your inner cheapskate. Pick a guitar that you like the look, sound and feel of, then come down in price range if you really need to.
To get some idea of the range you could be looking at, the Alvarez Masterworks Series MC90 Classical Guitar, a more pricey...