...essentially, assuming you're comparing mahogany sides and back and spruce top construction, the major structural difference between the two that may have the most effect on sound would be the bridge placement ... on the 12-fret, the bridge is further away from the sound hole and closer to the end which centers it more into the middle of the lower bout ... the 14 fretter has the bridge moved up closer to the sound hole ... in my experience the 12 frets are more scarce and it may be tough to A/B 12 vs. 14, even at large guitar shows or vintage shops ... if you search the forum, you'll find more discussion on these ... bottom line is 'sound' of a guitar is a very personal choice, and it helps to be able to play quite a few before settling on one you like ... I've owned a few each of the 12 and 14 fret over the years, but stick w/ a particular 12 from the early 30's, although I've played some really sweet 14 fretters in shops and at shows recently ... good luck w/ your search...
