For distance, its best to get an external antenna as high up as possible. Since you didn't mention any particular band or frequency (the driver to what is the best antenna question,) a discone antenna will do the job.
Some of this is because of the design of the radio systems. Usually there is little reason to put effort into coverage outside of the agencies are of jurisdiction.
Depending on which towns and how far away they are, there may not be any antenna that will work.
Telling us exactly which agencies you want to hear would help us give you a better recommendation.