Depends.
Frag is always loose, unless we're going to a dock diving event and will be rotating in the car.
Recon and Patton are always crated when I have the crate in my car. It's very rare that I don't, but for the last week my roommate has been using my car crate for her sick cat, so I was sans crate. They just rode loose for the week. No problems.
Boarders, fosters, etc. are always crated in the car. I can't wait till I'm on the highway to find out that they want to come into the front seat and potentially kill us all, so I play it safe. Mine are taught to ride freely in case it's ever necessary so they know to lay down/sit and chill out.