If you are not worried about the extra $100, I would say it comes down to personal taste. Going in and playing with them is great, but I would buy one and take it home for a while. See how you like it after reading a few books on it. As far as I know Best Buy allows you to return readers within a certain amount of time (14 or 30 days?). Or if you can afford to, buy them both and return the one you don't like. I bought my Nook thinking I would just try it out while visiting my Dad in the US, I fell in love with it though.
I read mostly fantasy and I buy from all over. I find that B&N has the best selection over Sony and Kobo (and some smaller stores). I know with Sony you can use other ADE DRMed books, but I think you would have to do some stripping to use B&N DRMed ebooks on a Sony. I am not sure. With Nook you can buy from B&N and any other store that sells ADE DRM.
www.inkmesh.com the site Polly mentioned above is a great idea for figuring out what books are available where and for how much.