As you can buy the PRS-T1 in the store, I would go with that one. If you don't like it you can return it. The Kindle is fine too. Other than buying from Amazon the PRS-T1 is the most versatile as you can download, sideload, borrow library books, sort collections easier IMO.
I have 3 Sony's and a tablet, and I bought my mother a kindle last year. I used the kindle extensively while I was setting it up for her and the reading experience is great for the most part, but no better than the Sony and the organizational experience leaves something to be desired if you plan to have a lot of books on your reader or even if you don't. Amazon's support and return policy are better than Sony's but having experienced both readers for a fair chunk of time I have to recommend Sony.
Kobo and Nook are probably excellent as well, I just have not had the pleasure
Other than that just buy one and you will be awed and amazed and wish you had bought one sooner.
Helen