I'd put Castle in the Sky: Laputa in the first group. It's an amazing film as far as I'm concerned. Just the right blend of action, and story... and who DOESN'T want to find out they're the last of a ancient race of people who fly around in a castle in the sky.
Especially with those robots...
I'll agree that Howl's Moving Castle wasn't great, but I thought Spirited Away was good (but perhaps not as good as Nausicaa, Porco Rosso and Caslte in the Sky). For me his movies are ranked something like this:
Castle in the Sky: Laputa
Nausicaa
Porco Rosso
My Neighbour Totoro
Princess Monokoke
Kiki's Delivery Service
Spirited Away
Howl's Moving Castle.
Now, if we're talking about the Nausicaa manga... that's a whole different story. THAT is a true masterpeice of storytelling that blows all the rest of what he did after away. That's one thing that's always bothered me about the Nausicaa anime... it's just so much less than the manga. I would've liked to seem them do a series of OAV to do the whole story justice.
I don't really count Lupin: Castle of Cagliostro among "Miyazaki movies". True he did it, but he didn't write the story (or invent the character of Lupin III).