I picked the Trinidad Scorpion because it was at one time the record holder (Not at the time I ordered it, but still felt confident that it would be a respectable kick in the face). Also, they look cool. Of course they look cooler when they actually produce a pepper, but that's a complaint for another thread.
And not super, but my purples and peters were picked at the request of my fiance, anything to get her interested / tolerant of my hobbies is a good thing.