Mononoke Hime is definitely the one i have seen most times, Laputa is my nostalgia favorite, Totoro is the one i love to show to people who don't know Studio Ghibli, Pompoko and Grave of the Fireflies are my favorites not by Miyazaki, On Your Mark is my favorite music video by Ghibli (the song sucks though)...
...ok, you guys get it, there is something favorite in every one of them for me 
“It appeared that there had even been demonstrations to thank Big Brother for raising the chocolate ration to twenty grams a week. And only yesterday, he reflected, it had been announced that the ration was to be reduced to twenty grams a week. Was it possible that they could swallow that, after only twenty-four hours? Yes, they swallowed it.”
- George Orwell, ‘1984’