Great explanations 1usmc! I'm a big radio guy and that is a great summation of the mentioned radio types. As mentioned GMRS Radios are ok (By the way the FRS and GMRS Radios both are using FM modulation as opposed to CB's using AM mainly and SSB or Single Side Band which elminates the carrier and one side band from AM that suck up power and usability) and they do require a liscence which most people never bother to get and no one seems to care. They still arent' great but do fine for off roading.
SSB: The problem with the CB's that have this great feature (SSB is pretty much the only mode I use my HF HAM radios) is that not many others have this ability. It does give some greater distance as the same amount of wattage is put to a better use.:
In this photo you see an AM wave. Imagine your CB radio is putting out 12 watts (that is an approximation of what they actually put out but only 4 watts are usable) the center line called a carrier gets 8 watts, the top line or upper side band gets 2 watts and the lower side band gets 2 watts and the 4 watts from the sidebands are the audio you hear hence the 4 watt legal limit. You can't actually hear the carrier only the side bands. When you remove two of these parts of the wave using only a Single Side Band you can use all 12 watts for the actual audio part of the wave and the radio will reconstruct the other side bands so you don't hear something that sounds like a duck quacking. (It's pretty funny to hear when it's not reconstruced)
So yes it's a more effecient way to send out your power but not many have the ability to do it that aren't radio nerds like myself.
FM is much more pleasant to the ears than AM but uses up more power for the signal. Thats why the FRS/GMRS sound so much better. If you want to get the most distance out of a signal (being realisitc now and referring to only the immediate area because a SSB wave at the Right freq can travel the world anytime you want if you know what you're doing[shoot me an email if you want more info on Amateur radio and how we do this] a 2 meter (144-148mhz) amateur radio using local repeaters gets the most distance. Most well placed repeaters can let you talk for a good 50-100 mile radius. The only issue is you have to talk your friends into getting a HAM liscence as well to talk to them.
I'd get a regular CB and save the money and have some FRS/GMRS radios handy and you'll be able to talk to anyone on the trails.
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