Have you seen Toy Story 3?

My neighbor Totoro wins by a very slight margin. 

So far Iv'e seen:

Nausicaa of the Vally of the Wind,
Grave of the Fireflies,
My Neighbor Totoro,
Kiki's delivery service,
Porco Rosso,
Whisper of the Heart,
Princess Mononoke,
Spirited Away,
Howl's Moving Castle
and finally Ponyo.

I uh... was making a plan to watch every single film they've made, but I slacked off a bit.  

This is like asking to pick your favorite child; it's that tough.  Either Grave of the Fireflies, Princess Mononoke, or Howl's Moving Castle.

Nausicaa, just because of the terrific quality of the animation.

Spirited Away, easily.

2nd Favourite is a tie between Totoro and Howl.

Pompoko gets an honourable mention for being so totally weird.

Howl's Moving Castle, just because it is perhaps the most beautiful full color hand drawn animated movie I have ever seen.

Grave of the Fireflies was seriously touching though. Strangely, Princess Mononke is my least favorite because I have no idea what was going on during the film at all.

So hard to answer... I love Spirited Away, Grave of the Fireflies, Ponyo, Howl's Moving Castle... I still have to see a lot of Ghibli movies.

Howl's Moving Castle and Kiki's Delivery Service.

While I like most of the others very much, these were by far my favorites.

Castle in the Sky is still my favorite followed closely by Totoro...

Kiki's Delivery Service is mine. I think I've seen all of them except for Ponyo.

Second favorite is probably Howl.