Ans:
Consult with ARGO Engineering as early in your design process as possible.
Remember that at some frequency which varies from manufacturer to manufacturer, the use of an overtone is mandated.
Remember also that within a certain frequency range, the fundamental frequency and the overtone frequencies may overlap. In such a case, your selection may be determined by your application.
If you are developing an oscillator that is to be extremely stable and accurate, with a high "Q" value, you probably need an overtone. If you require a lot of pullability, you probably need a fundamental.
Again, consult with your crystal vendor as early in the design process as possible.
