This is just my opinion, but of the 3 carrying methods mentioned here (internal, under, on the back), I like the under option the least.
My families last 2 large vehicles, a 90 Aerostar and an 88 Plymouth Voyager, both had full-size spares mounted under the back of the car.
If you end up not using them, it gets bad, real bad.
My dad and I had to cut the one off the Plymouth because the wheel and brace (holding it in place) were rusted together.
The Aerostar's tire actually fell off in a parking lot. My dad came out and started pulling out of the parking space when he hit something. When he couldn't see anything out the window, he got out and found it.
The single bolt that held the tire in place had completely rusted, and just snapped. Good thing no one was driving at the time.
Not I have a 99 CR-V, and I rather like having the wheel on the back. I still have an internal wheel well in the back, and I am able to store an blanket and pillow (for emergencies) in it.