great poll. i voted military craft. why? because it's the most likely answer. i'm certain the US military has made technological advances in the last 50 years the likes of which we couldn't begin to imagine. furthermore, art lives next to a military installation where test flights are routinely carried out. if we were to have seen a stealth bomber flying around before its existence was made public, we would likely have concluded it was not earthly. and many people DID reach that conclusion. ufo reporting organizations were riddled with calls from people who reported what later turned out to be the stealth. and today, the concept behind even the stealth bomber is old technology.
in every ufo sighting, the most likely explanation is that it's an earthly craft, and in each case, it's what you have to believe (IMO) until proven otherwise. i have a feeling a few military guys from groom lake got a good laugh listening to art talk about what he and ramona saw.
from wikipedia article on Area 51: "The base's primary purpose is to support development and testing of experimental aircraft and weapons systems."