For me it was worth getting a tow bar fitted on my car just so I could attach a Thule tow bar bike carrier. So if you already have the tow bar fitted then in my opinion a Thule tow bar bike carrier is the only way to go.
I agree re fitting tow bar, if you are likely to use the thing frequently. Re the rack itself, I went for the basic £180
Halfords jobby, as it's incredibly simple but strong. Yes, the downside is you can't open the hatchback when it's on, but given that it was over £300 cheaper than the Thule, I can cope with packing the car carefully so that I can retrieve stuff from inside the car. It's done about 10,000 miles fully laden on various cars, and not once has there been any worry about the safety of the bikes. The only tiny damage one time was when a pedal from one bike left a small scratch on the frame on another, from not having been secured in the right position. It also comes off in just a couple of minutes, and packs down very small, so it'll go under other things in the back of the car.
Here it is at Alpe d'Huez:
