I had to introduce my friend to it and shes always so hesitant (it kinda makes me mad honestly 'cause I'll ask her to watch something with me and she'll refuse, then she'll watch on her own months later and talk about it all the time, bugging the crap outta me lol) but she watched Howl and I think she enjoyed it.
Hmm. Kiki was my first (before I even knew who Miyazaki was!) Spirited Away was when I got really into it. The only ones I own are Howl and Ponyo but I think my favorite is actually Ponyo haha.
Howl's is based off a book with the same name. I read it in middle school and I totally suggest it if you haven't read it already. ^^ I think Castle in the Sky was also based off a book but I haven't read it.