Well okay...technically I have only ever watched Spirited Away and half of Howl's Moving Castle (I intend to watch the rest when I have finished reading the book), but Spirited Away was excellent.
Oh god this is a hard one.....umm can I say all of them? I've only seen
Spirited Away
Kiki's Delivery service
Tales form Earthsea
Porco Rosso
Princess Mononoke
Whisper of the Heart
The Cat Returns
Howl's Moving Castle
My Neighbor Totoro
I plan on watching all of studio ghilbli's films, out of the ones I've seen I suppose the ones that really stood out to me as really good were...well all of them, I guess I didn't really like Princess Mononoke (but I loved the message), and Tales from Earthsea (I don't really know why). Just didn't like these ones as much as other Studio Ghibli films.
