evergone

i personally play both martin and gibson. both companies make outstanding instruments. it may be that jeff or the sound techs get an idea for the acoustics of the building, then get an idea of the tone they want a certain song to have and choose the guitar which will suit the need. often, martins have a huge bottom end when amplified which can be a bad thing depending on the type of room you are playing in. gibsons tend to have a much more even tone. my humble opinion...