recently did a project using the adafruit electret boards with a max9814 onboard amp. they were surprisingly good and sensitive to my ears given the space they were set up in. the amp being on the board with the mic helps reduce noise, and the auto adjustment in volume levels can either be a big help or a pain depending on what you want to do with the mics, its almost like a really primitive auto compression. the whole set up is still pretty sensitive to power supply noise, so probably best with battery power than direct from a USB.
