CB radios use a set of frequencies that are channelized. You pick a channel and talk. CB is a easy entry radio. You do not have the versitility of HAM frequency selection etc but it can be a decent choice for some sorts of communication. Range wise it beats the FRS radios by miles depending on your output power and antenna, but again everything is dependent on being able to reliably connect to the party you are interested in talking to.
CB is using frequencies similar to 10m ham bands. This band can have some interesting long distance connections, but is not used for Reliable long distance communications (100's of miles).
FRS radios are generally limited to 1-3 miles in good line-of-site communications. A decent HAM VHF or UHF radio can do much better in line-of-site, and by using local repeaters can in many cases do 30-100 mile reliable communication. A repeater will also allow communications over hills etc...in other words you are only dependent on line-of-site to the repeater.
I do not know what sort of ranges CB radios are good for.
Ham allows frequencies that can do worldwide comm, so it is your best bet overall, but a serious evaluation of your needs is required to pick the best options.
CB for car to car in the same general terrain should be good, vastly superior to FRS, you will be limited to the 40 or so channels though and may or may not have a clear frequency depending on local use.
Remember that you can use HAM frequencies without a license in an emergency. So knowing your local repeaters, local ARES/RACES/ACS groups should be part of your preparation. Listen and learn, transmit in an emergency and you will be AOK with these groups and the FCC.
Another thing to consider with your FRS radios (and any other radio) is a decent external antenna on the cars. The short stubbies supplied, operated from inside a car are just barely adequate. Getting an antenna for these frequencies mounted on the exterior of the car may improve comm considerably.
Good luck.