Having experienced most methods of carrying a spare wheel over the years (all of which are listed below) I have to say that the swing-away carrier is by far the best and easiest to live with.
Standard rear-door mounting is ok but it does strain the door & hinges over time and can limit you on the size & type of wheel / tyre combination you can fit.
Roof is a last resort as many people would struggle to lift it up / down safely, you would need some sort of carrier / roof-rack and of course the COG & drag is increased. Not a good idea in my opinion.
Internal is great as it is protected from the sun plus is relatively secure but it does take up a fair amount of space
Bonnet keeps it out of the way but if it is a wide tyre and you are short then you will struggle to see over it. Add to the equation that some people would struggle to lift the bonnet (which means that regular checks may be postponed) and it is not an ideal solution for everyone. Also you need the correct mount and (even more important) the correct stay.
The Pivlock was about the first commercially available swingaway carrier around, it is independent of the rear door and can be locked in the open position. Works fine if you only ever have to open the door from the outside but if you carry passengers in the back then it means that it is impossible to open it from the inside with the carrier in the closed position.
After that all manor of manufacturers got in on the act and now you have a wide choice of swingaweay carriers, they all do more or less the same thing but in different ways and some with a greater degree of sophistication.
This is my WH carrier which has given 15-years of faultless service (it is a normal rear-door model but just connected to my side-hinged tailgate).
I had it galvanised a few years ago as the original powder-coating had given up the ghost but apart from the occasional squeeze of grease into the nipples and a squirt of WD40, that is it.