I would have to say that I enjoy both, but only certain genre's. I love adult mysteries, because one: there are more adult mysteries then YA and two: they're usually very focused on the plot aspect, which I love. So if there are two characters you want to get together in an adult mystery you better have some patient because it won't happen for a while. :P Not that I haven't found clever YA mysteries, I have they're just not as abundant. In YA, I love reading fantasy/paranormal (there's an overflow) and regular day in a life comedy novels.