I have to go with hands down America. I'm not a huge fan of foreign horror but I definitely check it out as often as possible. (loved Ichi, Ringu, Bava, Most of Argento)
I think I prefer American horror because I fully understand it just on a cultural level. I can't relate to the J Horror and the ghosts because I don't have that desire for nostalgia or strong ties to my family (i.e. failing the family name by not becoming what my parents envisioned). My family gets along great and all, but the point is from a cultural understanding, different cultures are afraid of different things with examples here:
Invasion of the Body Snatchers - Cold War/Communism
The Thing - AIDS
They Live - Regan, Anti establishment
Exorcist - Loss of a loved one
these films can all relate to me on some level that i feel i don't get from giallo or j-horror. Thats just me though I guess