Only issue with boot carrier's is that it is really hard to stop the wheel etc rubbing on certain parts of the car marking the paintwork.
The best ones to have are the tow bar ones, i used to work in a bike specialist shop a few years ago these where the best we used to sell.
http://www.maxxraxx.co.uk/home.html
Obvously you may not want a tow bar fitting though.
I had the same issue with the Astra due to the rear spoiler i could not get anything to fit correctly.
I am sure things have improved since i last looked and i have heard good things about these racks.
http://www.evanscycles.com/product.jsp? ... gn=froogle
Your best bet is to go to a decent bike shop that stocks a wide range of racks and test them out. I would not really go to your halfrauds unless you have to.