I have a big jar full of plectrums in the studio, so I have a lot of choice when it comes for acoustic guitar sounds, an example for this is, when I want to double up an acoustic guitar recording, I always use a plectrum with a different thickness, in that way you get a completely different sound from the second guitar, which can create more separation in the stereo picture. Or if it's a single acoustic guitar that I am recording, the plectrum choice can really alter the sound of the guitar, so I choose a plectrum that will help the guitar fit in the mix I am working on.