Personally, I'm looking at Microsoft Surface Pro 2 instead of any tablet, because it's not just a tablet, but an x86 PC that can run Ubuntu (yes, 2, not 3, because larger size and loss of Wacom digitizer while retaining the same hardware don't look like improvements to me). I even think Apple will present an "iPad Pro" along these lines, this year, with a killer feature of being able to run OS X apps. I don't live in Apple-land and I don't want that, but it should be popular.
If you are so flexible as to consider Android, iOS and Windows, you should consider Microsoft Surface Pro 3, too. I am really interested to know your opinion; my email is in the profile if you will actually look into it and decide to share. For me, Microsoft tablets are an overseas shipping order away, so I hesitate a lot before buying a completely new piece of hardware.
Personally I was all set to get the large form factor iPad but will get a Samsung Note Pro instead.