The number of cranks is the same face down or up, just your starting and ending points will be different.
Your question got me thinking about a time when I had a spare behind the back seat of K5 Blazer I had. The spare was face up laying on the floor. My Lab had a blanket I would lay on top of it for her to sit on. One day my Lab jumped into the back seat (Which she never, I mean NEVER did.) followed by a loud hissing sound. She had sat on the valve stem enough times that it broke off. It was funny as hell. But back to the question...
If I had a choice it would be like it is, face up.
As mentioned before; it is more protected, will hold less dirt, the T bar won't rub anything you will see, and when you drop it on the ground & slide it out from under the rig, you won't scratch/rub/bend anything of importance (like the valve stem

) on obstacles. (Like large rocks if you are off road.)
