As mentioned above, both have their place, and are completely different animals.
FRS is perfectly usable car to car within about 1/4mile, maybe a little more. Out in Quartzsite you can almost talk across town on them. They are quiet, and you can program them to lock almost all other traffic out.
CB on the other hand suffers from allot of issues, one being the 11year skip is in and at its peak. During the day you will be lucky to talk as far as any good FRS radio, and really stand a better chance of talking to someone 1000 miles away than the car in front of you. Nighttime is different as the skip is out, but it's by no means completely gone. People complain and whine all the time about truckers and language, but the simple solution is to get off of Ch 19 and 6, where 99% of that traffic is and problem solved.
With the prices of either these days, keeping both on hand is not an unreasonable option