@Dan
If you want to go mobile and listen to VHF airband then you'll need a portable. If you want the best then a secondhand Yupiteru VT 125 or 225 would bring best bang for buck or alternatively a Yupiteru 7100. Any of the Bearcat or Whistler branded scanners would do the job and a lot depends on whether you want alpha tagging (displays the station name as well as the frequency), many of the cheaper ones don't. Also if you're using the scanner at home, do you have an external antenna, you may not receive some stations if not.