Ok, I was looking forward to stock up on piezos. Not particular plan in mind at the moment, but I just want to have them around when I need them. (shipping times are bothersome) So, I was looking for me most versatile ones.
Then, I've realized that I know next to nothing about piezos, but when looking around on ebay, what it seemed to vary was the size of them alonside with the resonant frequency.
So looking for resonant frequency of the piezos I've found: