Peter, first off 2 meter HAM is FM & CB is AM, so 2 meter naturally sounds much better. Any simple 2 meter radio with any off the shelf antenna is going to outperform The average CB setup at short distance communications. Sure CB can has the potential to make across the world communications, but that's not the goal of the off-roader who just wishes to talk to a friend who is a few miles away.
Mike, I didn't expect an answer _this_ simplistic from you. Here's my take, Kennith-style; Mike W will likely respond in about a week with something "for Chrissake, a radio is a radio" (all in capital letters), and he will be right.
First, quality: both CB (AM) and 2-m ham (FM) use 10kHz bandwidth. It translates into roughly 4kHz of usable audio band, and therefore the quality should be the same. In absence of static, it _is_ the same - I'd even say I like my $40 CB unit better. Here goes "2 meter naturally sounds much better."
Next, range. A typical 2-meter mobile unit has 50W transmitter output, and the antennae are shorter (in terms of fraction of a wavelength) than CB - giving a ham mobile transmitter a huge advantage in power density (Watts per steradian). However, there are three disadvantages I can think of:
- 2m is much more of a line-of-sight communication band than 12m CB, although you can get pretty far on the fringes of diffraction/refraction pattern; you can get very long-range reception with a CB box and tuned 4" Firestik;
- narrower directional diagram of an antenna means more frequent loss of communication when your antenna is slanted (which happens off pavement) or your other party is at a significantly different elevation than you (which also happens);
- the noise figure of a receiver at 2-m band is typically worse than that at 12-meter.
I am not going to talk about the additional benefits of having a ham radio - like using the repeaters or APRS or [insert your particular joy of ham license].
But, to sum it up, for trail use I have not yet found any considerable advantage of using ham radio - except for handhelds. FRS? meh. Kevin is right on the money here.