Had some fun with Wikipedia and Excel during lunch. UFO sightings during the 20th century. Admittedly, it was the English version of Wikipedia. Results attached.
It would seem that given the choice, Aliens prefer to visit:
- English speaking countries, and in particular
- the Western Hemisphere, and in particular
- the US
While here on Earth, they obviously like to:
- entertain the population of the 5-Eyes Spying Club member states
- avoid Continental Europe and Asia if they can
Each of the above by a surprisingly ridiculous margin.
Why would they do that?

Edit: African Sightings are the coolest:
Southern Tip: 13
Rest of Continent: 1
http://en.wikipedia.org/wiki/List_of..._UFO_sightings