I think Mononoke? I know I had seen the Ghibli logo in previous "affiliated" movies, but I don't think I'd seen a legit in-house production from them before that. It's a wonder the movie is not my favorite. I honestly think I probably enjoy it a lot more than the others. But my favorite is Nausicaa (as Mo said, not really Ghibli, but you'd really have to split hairs to legitimately argue that. Basically it was theirs just before they had that particular name). Nausicaa isn't actually as entertaining as Mononoke, but there's a lot more I appreciate about it. The drama and characters are a little more realistic to me. Mononoke is more of a good fantasy. But a lot of those things wouldn't actually happen if that were a real world. The things in Nausicaa I can totally see happening. The attitudes and struggles and character developments. Miyazaki had a craft in legitimate drama and subtlety that most of Japan struggles to create even to this day. And I still call them out on confusing melodrama for real drama. They all should have taken a page from his book