A couple of bits & pieces I've picked up over the years using RT's for work
Your choice of arial length, go see taits or someone similar. The length of the arial will affect the tuning on a base unit (car mounted) best to talk to the pro's about it.
As for the hand helds, compare wattage, the stronger the watts the better the unit will deal with hills and gulleys, cheap ones (low power) are line of sight and even dense scrub can affect them, the more power the better so they can bounce signal off hills etc
Oh and if your after second hand FM units

try the trucking companys they upgrade all the time
Cheers Reece