I use a matched pair of Neumann KM-184 for most of my classical guitar recording. They're tiny, extremely sensitive and accurate and respond well to the smallest changes in dynamics, nail angle or right hand position. So if you're playing clean, they give back what you played in spades. But if you're a little sloppy, the sensitivity reveals finger noise and lack of tonal and dynamic control shockingly well. I like using them about two meters out in X-Y on a Shure A27M Stereo Microphone Adapter. Much faster and easier to set up compared to a stereo bar or two stands. http://www.fraryguitar.com/shure_a27m.htm
If you want a sensitive mic that's a wee bit warmer and forgiving, check out the Neumann TLM 102 MT. I only use mine for multi-track projects but really love it's sound. I plan to buy another one when Mr. VISA is feeling a little looser.