Has been a very interesting thread. I still vote the rear tyre carrier though, Mine is right smack bang in the middle. and visiability is poor, between the tire and very dark tinted window it is very hard to see out the back, that's why I'm mounting a reversing camera to a mirror monitor running permantly.
My tyres are 33" and my spare is 31" which needs to be updated, plus I'm thinking of running 35" tyres including the spare so visiability will be even worse. So a camera mounted high looking down will give me everything I've lost. Mounted another reverse camera just above towbar whilst in reverse which will be perfect for reversing and seeing how close you can get to other cars and objects without hitting or guessing how far you are.
I see the biggest complaint is, its a pain to move the tyre carrier to get to the back, well I need the 3rd row of seats (not all the time though) and there isn't much room behind 3rd row of seats, so I've got tools and spare, and as for shopping I place in behind 2nd row of seats by putting seats down from back door, too easy.
I'm surprised that no one has come up with an auto open and close tyre carrier yet (could even set it to a button on your remote for you alarm, if you have spare button etc, could use air, electric, or even electric over hydralic, I couldn't imagine it would be too hard to do
my 2cents
Jas