Landscape, seems pretty silly to hold it in portrait mode really. At least it does to me. Size doesn't matter to me either large or small I hold it in landscape because Web pages just fit/look better.
On some games and some apps I don't get much of a choice though.
Hate the iPad keyboard in landscape though, it's either too small (split) or too large. Wish Apple would allow keyboard customization with programs like SwiftKey or thumb keyboard.