Well, since it's VHF, you could go with a quarter wave, 5/8 wave, or maybe one of those Phantom "soup can" type antennas.
For a SmartZone system with almost perfect mobile coverage, you don't need anything above what the OPP has on their vehicles for an antenna.
Are you trying to get distant towers when you are in your vehicle? You may find that a simple quarter wave is more than adequate.