Frequency and legal restictions are the difference. I have had all four. Aviation doesnt require a license any more, but you had better be a pilot conducting flying related business. Marine VHF doesnt require a license, but the same goes for it as for aviation. Marine HF requires a license. ( mine needs renewing) CB, well, its about useless. <br>The most bang for your buck is HAM. It requires a license. You have to pass a written exam to get in on the ground floor. I personally feel that a handheld 2 meter radio is much more versatile than any cell phone in an emergency. I modified mine to do marine also, but its not legal to use such a modification unless you are protecting life or property.