I vote for an android platform I have an old galaxy tab 10.1 and still use it frequently, my wife has the original kindle fire and is in love with it. Paid 399 and 199 each when they came out. As far as apps go you can honestly get pretty much any app on either OS.
Another thing to look at is the microsoft surface. Looks pretty sweet and has more under the hood than most other tablets out there if not all of them. and so far I enjoy the windows 8 platform on my laptop. Very easy to use. I think its 499. Only problem here is slow support for apps but with a projected 4 to 8 million expected to sell this year (foxnews.com cant remember the article name) it is sure to pick up, not to mention with laptops having access to the same apps that adds in huge numbers to people able to use microsoft apps.