Now this is my favorite! I saw a wide version of this poster on a Japanese website of dubious quality (the site claimed to sell movie posters, but was extremely sketchy on details), which I've completely lost. But I absolutely loved this poster and it's easily my favorite of all the Nausicaa posters.
The reason I love this one is because it seems more closely tied to the Nausicaa graphic novel. The image of Nausicaa on Kai (the Horseclaw) reminds me of the epic 40-page battle from Volume 3. It's a tremendously exciting and emotionally exhausting read, and requires just as much buildup as the actual battle itself. And the ending is sudden, shocking, tragic, brilliant.
Oh, and the movie is terrific, too. I'm sure you know that already, so no more preaching from me.