I like most of his movies equally, come to think of it... basically I couldn't enjoy Ponyo beyond the visuals and moods, which I loved, and I find Howl too long for its own good. Kiki's Delivery Service is surprisingly entertaining for such a sparsely layed out plot (much like Totoro, but that's better)
Nausicaa, My Neighbour Totoro, Laputa (Castle In The Sky), Porco Rosso, Princess Mononoke and Spirited Away are pretty much perfect to me, and I can't even rank them. I hope Mr. Miyazaki gets to direct a couple more, especially the follow up to Porco Rosso which he really wanted to make.