AFAIK FRS radios cannot be used with an external antenna. Given that, I'd say CB is a better option just because a CB with a decent antenna can reach out far enough to talk to anybody else in your group, even if someone is as far as a mile or two away.
If you don't want to do a permanent install of a CB you could use something like the Midland 75-822. I've been using one for years. With an external mag-mount antenna on the center of the roof it works pretty well, with a permanent mounted (and tuned) antenna it would do even better. The entire unit is contained in the handset and it plugs into your 12v dash socket so there's no wiring to mess with. It also features 10 (I think) WX bands so you can get weather in many areas.