Need a multi-choice poll, because I have all three.
CB is nice on the road, and occasionally on the trail when you have some distance between parties.
GMRS is great for spotters and groups using bubble-pack radios.
Ham (VHF/UHF) is great for longer distance emergency stuff, as long as you take note of any repeaters prior to entering an area. There are some great apps available for phone usage that can show you repeater freqs and geo-locations.
I use amateur radio... when spotting, on the road, trails, emergencies! Using APRS in my radio, when I can, to let family/friends know where I may be and that I'm still moving along alright. It's really a do it all thing!