Depends on your tastes and what you are looking for but I think the selection is actually quiet good. Almost all new release are coming out in e-books now and a lot of older have been converted. Before I bought, I wrote a quick list of ten recently published books I thought I might like to read in various genres and I was able to purchase all 10 electronically.
Google and other groups have taken all of the "classics" that have become public domain and you can revisit all of those books for free or something close to it. When it arrives, I needed a test so I downloaded the entire library of Sherlock Holmes books for 89 cents.
Amazon has the most the most books available at over 250,000. B&N claims the largest library (over 700,000) but the trick is that they include the public domain (freebies) in their count. Amazon has over 810,000 if you include the public domain titles.
However, there is shareware that will convert the various e-book formats to another so not a big deal worrying about who has greater numbers.
I had some e-pub book that I downloaded during my tests to see if I could study from my laptop or Sharon's iPad but I couldn't hack long term "reading" on an LCD screen (despite working all day on one). e-Pub is about the only format the Kindle doesn't naively support but I used freeware called Calibre to convert them and they moved over perfect. I didn't feel bad about breaking any copy-writes in converting them as they were public domain books.
The text to speech features might be handy for you too. I might try it out to listen to a novel during my next long drive.
Speaking of which, I coincidentally had just finished another post asking you for some advice on speech to text.
