The temperature and general weather in your area is a key thing to consider that most people forget about when buying a car-friendly crate. If you live in a hot climate, you should think about getting a wire crate. These will naturally allow for more airflow. Though, most of these products don't feature a solid roof. Keeping a towel overtop may protect your dog from the sun whenever exposed.
Plastic crates with solid walls or other zippable and mesh products are great for those in colder temperatures. This will keep them warmer while transporting your dog and waiting for the car's hot air to warm up.