I am not sure to be honest and this is a good question. One of the things I have been toying with is the diety of Jesus. I simply don't agree with the org. that Jesus is simply an angel and first born son of god. While I still like the bible its mostly for the principles of kindness and love that are promoted within it. Doctrinally I think you can make it prove whatever you want it to with some careful thought and cross references. I have done this and I have come to the conclusion that Jesus is more than what the WT says he is. They also have managed to change meanings of some verses with some substitutions and omissions of their own, the same things they have accused other translators of doing.
Other than this I havent really given most of their doctrines much thought