I almost exclusively use it in landscape mode. It is easier to hold and I feel stuff just looks more natural in landscape: webpages, movies etc.
Thoughts?
OP, do you have an iPad mini?
I'm guessing a person's preferred orientation depends on their iPad's form factor (original 1-4, vs Air, vs Mini) and what they do with it.
For example: I mostly read or browse on my i4 in portrait. The i4 portrait screen is wide enough for readable text. Using portrait means I scroll less.
OTOH, I rarely browse on my comparatively "small-screened" iPhone 6. When I do, I flip to landscape for bigger text.