Generally, should I watch "Trailer 1" or "Trailer 2"?

When I go to watch a movie trailer at http://trailers.apple.com/, I’ve noticed that many of the movies have a Trailer 1 and a Trailer 2 (along with a teaser). I’m never quite sure which to watch. Is Trailer 2 the newer trailer, that better describes the movie or tests better? Or is it more geared for people who’ve already seen Trailer 1 and want more?

If you’re only going to watch one trailer, which is best?