Apartments are kinda fun when I just want to do a small reno/redecorating job and don't feel like putting a lot of time into building a house. But I really hate how hard it is to design layouts in apartments, because you're unable to move things like windows and other random objects that come with the lot, like the exposed pipes, etc. And also when you try to hide those with build/buy mode objects, you have to frequently move them out of the way to fix them when they break down, which annoys the hell out of me. I love those cute, shabby, cluttered apartments, but they're a pain to play in.
So yeah, houses are definitely my pick.