Mine would have to be The Girl Who Leapt Through Time. That was the film that turned anime from an interest into a passion for me.
Summer Wars is a big favourite now too; that's one I enjoyed more and more with repeat viewings.
Wolf Children... not so much of a favourite. I just don't connect with it, I guess. Although there is that one scene with the deafening silence (
that scene) that's harrowing to watch; outstandingly well done.
The montage that gives us a highlights package of Hana and the wolfman's relationship I find less successful. I think those kind of things are difficult to pull off and make the viewer really connect with, compared to perhaps depicting one little special moment that would sum it all up instead.
I find Yuki to be a character you can get behind, though; Ame... hmm. I'm not keen on him.
The Boy and the Beast is, for me, utterly outstanding as a film. I just love the relationship between Kyuuta and Kumatetsu! They're always at odds with each other — both being so stubborn — and it's all very fiery and explosive, but you can tell they still both really care. Kumatetsu is a hilarious grouch.
I guess if I were to rank Hosoda's film, then, it'd be:
1. The Girl Who Leapt Though Time
2. The Boy and the Beast (a close second)
3. Summer Wars
4. Wolf Children (easily last for me)
Looking forward to seeing Hosoda's next one, Mirai from the Future.