They are almost always better, especially the latter.
While it's stupid that trailers give away the whole plot sometimes, I can at least get why they do that, instead of going with something simpler, but for example, does anyone honestly think that the main poster used for Episode I (not that it was bad or anything) was better than this:
http://www.impawards.com/1999/star_wars_episode_one_the_phantom_menace_ver1.html
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"Ahem! There is *sand* on my *boot*!"--Kefka
Black Turtle beat me, Yesmar in the Fall 2010 Guru Contest!