I advise that you decide how you will use the device and what is the primary reason. The Kindle and the iPad have different purposes. The Kindle is a cheaper reader and its smaller size is convenient. Compare how much they weigh. My Kindle is 10oz. The iPad 2 is 1.3lbs and the new iPad is 1.45lbs. Too heavy and it won't be comfortable holding it where I like to read most often - in bed at night.
I have an older 2nd Gen Kindle
and have used it for a couple of years now. I love it just for the fact that I don't have to store all my old books in the basement anymore, am able to travel with all my books (numbering several hundred) and can download a new book anywhere. Mine has the free 3G, but that is only good for downloading books. Other units have the wifi only and that is fine if you have access to wifi all the time. We often don't.
I am probably going to get the new iPad shortly and can compare the two at that time. I'm getting an iPad in order to access the internet better than with my phone, download movies and pictures, etc. I'll also use it as a Reader.