The really easy answer to that is, read all of them
I think they all have a bit to offer, and Blair is still a very important source - I respect his research, just not the conclusions he'd made. I don't mean to disrespect either him or Werner, but I have a lot of trouble taking either of them without a grain of salt.
One of my favourite reads lately have been Michael Gannon's books on the U-boat war ("Black May" and "Operation Drumbeat"). And as far as books for general knowledge, there's a lot of really good stuff here:
http://www.uboat.net/books/index.html/new_readers.html
The other great thing is that thanks to sites like uboat.net, these days you have access to an impressive amount of raw historical records. Even just reading through those can be really informative, which I've done a lot of (both for modding work and research, and just for fun).