Rear trunk rack for me. I used to have a hatchback, where it was possible to fold the seats down and transport my bike with the front wheel off. My current car is a sedan, which is a lot less convenient. That said, if you are headed to the start of a ride, it is typically much easier to use a rack, and a lot easier if you are transporting two bikes.

I know people with pickup trucks and minivans. Different story for them.