As the main trip organizer among my group of 4x4 enthusiast, I've had to decide which communications meduim is a requirement to have and which is 'good' to have.
Heres my $.02 on them in regards to the trips i organize (in order of preference)...
CB: all the regulars have it, works fine for 99% of off road situations, is relatively simple to install and learn to use.
GMRS: Almost anyone can get and use even though they may not have 'purchased' an FCC license. An external repeater could benefit the range but for most uses, the basic radio is sufficient. Only downside is they're so darned easy to loose one on a trip... well for me anyway.
FRS: Anyone can purchase and use one. Reception is crappy unless you're fairly close to each other, have line of sight, or an external repeater antenna. Like gmrs, they're also easy to loose.
2M/ham: great for longer range comms especially when you know and have programmed in the local repeaters. Only problem is fewer people in the group (especially newbies and non engineering/techie types like me) have them. Im pretty surprised the sale of how to dvd's for the various units isn't more brisk.