CB radio works well in populated areas, where cellphones are more likely to work. Amateur radio usually comes with a significantly greater investment in equipment. It's even more costly in terms of time, since you have to pass an exam to become licensed, where there is no licensing requirement for CB.

I'd suggest you carry a cellphone no matter what, as nothing is more useful if it works. Between CB and amateur radio, check to see which is more popular in the places you expect to be.