For acoustic guitar recording I use a pair of Warm Audio WA-84 mics. I have been using them mounted on a bar about 6-7" apart on a single mic stand, but recently I bought another small mic stand so that I can separate the two mics more, as others often do. I have not used the wider spaced method yet, but will during this next week.
A pair of these WA-84 is fairly cost effective,
about $750.
I have also in the past had good luck recording acoustic guitar with a pair of Audio Technica AT4050 mics. However, the small diaphragm mics like the WA-84 seem to do a little better job on rapid transient response.
- Glenn