With a Ham or CB radio you will be able to reach farther in an emergency which swamps the "normal" comms systems. Either of these are "connectionless" meaning that you press the button and talk and your voice goes out. Your signal with CB will be limited to something like 5 watts output while Ham gear can and usually does run around 50 watts in a mobil rig. The HAM lisence grants priveleges to run much larger wattages than that but you wouldn't want to stand near the antenna or have it mounted on your car roof.

With Cell phones, if you get a connection, you can speak with exactly whom you want. With radio you will get contact with whatever Yahoo happens to be listening on the frequency you are shouting into. With CB that will usually mean truckers. They are generally helpful and knowledgeable of road conditions and routes. With HAM you will probably be able to reach the emergency communications that are set up for the use of FEMA or local emergency management. While this may not be a place for you to talk a lot you will definately be contacting the right folks. And you will be able to listen to them as well. It's a matter of coordination and frequencies.

I recommend that you get as much comms gear as possible. Start with Cell phones because they are cheaper and no training is required. Get a HAM lisence ASAP. There are weekend courses given around here (NH, USA) that provide the opportunity to test at the end of the weekend and almost a guarantee to pass. After you have your HAM lisence you will be free to evaluate CB vs HAM yourself. If you have the $$$$ and I mean $$$$$$$, get a CB, Multi-band VHF/UHF mobile HAM and a 6 meter or 10 meter HF mobile HAM rig. Then for monitoring the local emergency services you might want to add a trunking scanner but that is really big $$$$$$$$$$$$ for just a receive device.

If these words make no sensel, read them to a local HAM and you will be in for a weekend seminar that you might find really enjoyable but are sure to find informative.