I've had both a carcoon and an air chamber, both do the job well.
Pros and cons for both.
The air chamber is a fixed structure so you can simply drive in, where as the Carcoon has to zipped over the car. Air chamber is bulky and does take up a lot of space while only allowing limited access, but as its fixed its simply drive an go. The Carcoon is a bit more fiddly and it will take 5 -10 minutes to get your p&j in an out. But when down does give you plenty of space to work on the car.
