I'm half way tempted to recommend getting a hand held, then buying a external microphone, external car antenna antenna, and cigarette lighter adapter for it. I have a CB in my Jeep, and there have been occasions where I really wished I could have taken it out and walked around with it. Additionally you will be able to use it without any permanent modifications to your vehicle, and it will be easier to transfer between vehicles.

However, the hand held unit, will not be as convenient for in car use (more parts and wires to deal with, and the speaker may not be as loud). Additionally this set up will cost more than a standard mobile unit. A real judgment call based on what you think you will use it for, and how much you plan on using it.