A lot of apps are meant for landscape mode, it feels more like an iPad when I hold it sideways instead of in portrait mode. If I don't it just feels like an enlarged iPhone lol.
Landscape, almost exclusively. It's the full sized keyboard. I can't touch type on the keyboard in portrait orientation, whereas I can in landscape. I've never been a fan if thumb typing.
I also prefer reading in landscape. I like the look of an open book with two pages facing me.