I think much of the mud community would say get a Ham license and 2m radio/antenna.
But that doesn't work for all of us as many local clubs still use CB predominantly.
So if you must go with CB, I think most would say don't waste a lot of money on the CB, but do buy a quality antenna. Check the FAQ or Slee's site for a common install in the ashtray location. The all-in-one Cobra 75wstx is also popular. As for antennas, taller is better (all other things being equal). But a good install is even more important. Firestick and Wilson are popular, as are mag-mounts that get knocked off on the trail. In the end, if it is only for trail use, damn near anything will work as you'll never be more than a mile from the other vehicles.
If you want greater range for use say, at Moab when you might be a lot more than a mile away from your group or for long-range highway traveling, then back to the Ham license and 2m radio/antenna. License will cost you some time and about $14 for the test. You can get a radio for about $150 and an antenna for about another $70.
Good Luck!