You should try option 2 first, but sometimes if your jar is conflicting with pega OOTB jars (e.g., same jar but different version), you should try to include jar in the app server specific location, e.g., for tomcat under /lib directory.
For your external JARs to become readily available for the PRPC ClassLoader both at compiletime and runtime you will need to import it via the "Application > Distribution > Import" wizard.
Quick questions -
1) Was the server restarted after you imported the external JARs to the PRPC database table?
2) When are you facing this issue? Is it at compiletime (when your are trying to save a rule referencing the external libraries) OR is it at runtime (when you are execute/run the saved rule referring the external libraries)?
3) Also what is the ERROR/Exception you are seeing? Is it ClassNotfoundException or NoClassDefFoundError? Can you paste the complete Exception Stack trace here.