I bought a Martin D-18 in Brighton three years ago and it's still the best £1400 i've ever spent. I adore everything about this guitar, it's incredibly light and feels like a true piece of craftmanship. All of Martin's guitars are handmade and you can really feel that difference in quality and attention to detail.
When i first bought the guitar the action and intonation were perfect, the tone is beautiful and rich and the sound when played with a plectrum is resonant, full and with phenomenal sustain.
In the three years plus i've owned this guitar all of the above have improved to the point i can't play any other guitar, it just makes me miss my Martin.
Buying a guitar like this is an investment; as long as it doesn't get broken or seriously damaged the guitar will never be worth less than you paid for it. Martin guitars as little at a decade old are worth far more than they were in the year of production. I also have a Martin D-14 Dreadnought which is no longer produced and it's already worth a small chunk more than i paid for it.
If you've got the money and you're seriously looking in investing in a beautifully crafted instrument then look no further than the Martin D-18.
A beautiful guitar