This is sort of a two part question.

1) I've decided that whenever I have the money I'm gonna buy a new acoustic. I'm leaning towards a Martin because I love the rich tone of their mahogany guitars. However, I can't decide between the D-15m and the 000-15m. Both have the exact same price at my local store, and I'm not very knowledgeable in terms of their features. So could anyone with some experience give me a little direction? What are the differences, benefits, etc. of each?

2) That being said, this will be my first steel string acoustic. When I played a few different steel strings at the shop, they were certainly a lot different in terms of fingerpicking. So I guess my question is, is this just a matter of getting used to? Or are classical guitars really that much superior in terms of fingerpicking?

It's difficult to win unless you're bored.
My wife had one of the nylon-string Martins years ago, nice little axe. She played mostly folkie stuff on it.
Would depend on what you want to do with the guitar. The nylon-string is standard for classical music, of course, but also popular for a wide variety of other styles.... Latin music generally, Flamenco... Lots of fingerstyle jazz guys use them.
However the steel string is more versatile, perhaps. Steel string is standard for fingerstyle blues, lots of folk-type material, anything involving a flatpick...
I spend about an equal amount of time playing my little Taylor steel string fingerstyle and flatpicking... Works well for both.
i played classical guitars for years, and i don't find them superior for fingerpicking. one of the happiest things i discovered in my life was how much more fun fingerpicking is on steel - and i prefer how it sounds, too.

btw, i assume you've played guitars from the 15 series?
Quote by Skeet UK
I just looked in my Oxford English Dictionary and under "Acoustic Guitar", there was your Avatar and an email address!
It just takes the getting used to.

The difference between the D15m and the OOO15m is the size. The size changes the tone. The D is a larger guitar with a 25.5" scale. This gives the guitar more volume and a lot more lower midrange boom. They tend to be better for strumming around a campfire for this reason.

the OOO has a smaller body, more pronounced waist, and a 24.75 scale length. The smaller body means better single note definition but there is also less volume. The shorter scale means less string tension and, for a lot of people, less tension means a faster playing guitar. This is why many finger style players prefer the OOO.

Both are excellent guitars and can be used for almost any situation. I love the 15 series in all it's forms. Try them out and see which you like better because other than body shape and scale they have the same features.
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