I agree on Westsider. However, I always liked the Strand for its collection of history, science, and math books. While Strand can be crowded and touristy, it still has a good collection of books.
The last time I was in NYC, I was really hurting because of not one but two bad hamstrings cause by hockey. I could barely walk--which is not a great combination with NYC. I had some time and took a Circle Line cruise. It was delightful and I hadn't done it since I was a child!