swing-out on right?
Where do you want your spare to be when you pull off the road and need in the back? In North America, that's the right, and due to the crown of a road, the downhill side. Also, the spare is not on the traffic side.
The question becomes even more interesting with a double swing-out. Tire on the left or tire on the right? There are good reasons for each. The best part is, put it where you want it.
Oh, and edit to add, think about using tamper resistant screws on license plates. Recent plates seem to have a certain street value, at least around here. My rear one disappeared a few months ago. Just another DMV hassle, and more dollars wasted. My response was six screws and 10 more minutes of work. Google pulled up this:
http://www.brycefastener.com/
Dale