A nice crate where your cat is comfortable will help you to crate train your cat. If your cat enjoys spending time in the crate you will be able to easily get him into the crate for veterinary visits or quickly out of your home in an emergency.
A crate with a door on top makes it easier to access your cat. It also makes it easier for a veterinarian to reach in to get your cat as well (it is less stressful for a cat to be picked straight up than to be pulled out sideways).
A larger setup works well if you need to drive a long distance with your cat. If you are going to be in the car longer than a few hours, something with a space to use the bathroom is ideal.
Base Camp by Jackson Galaxy is such a cool idea. It turns the crate into a super fun place where your cat wants to go!