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I actually think the exact opposite: Princess Mononoke is slightly better. They are both my favorite Miyazaki movies, tho.
I can definitely agree with the last part. I just simply disagree with the order is all. Nausicaa is actually my favorite movie having displaced Mononoke. They're actually both the same basic story anyways. Just one is more sci-fi based while the other is fantasy based. (Main character is a peaceful person at heart who gets screwed over by the world being shit, finds a potential romance in a character who is technically an enemy in a way but turns out not to be, many of the characters who end up in conflict with the main character end up coming into conflict with them over morally ambiguous actions, main character saves everyone through self sacrifice. Although Nausicaa has Patrick Stewart while Mononoke doesn't, though Mononoke has some other big name actors and actresses.)