I used to be 100% convinced JW's were the only true religion, because I studied the Watchtower endlessly. It was not until I compared it to what other religions believe that I could see the dishonesty and inaccuracies. It is important that people in other religions are just as sincere about finding truth as JW's, and so have a good scriptural reasons for what they believe.
JW's know Watchtower doctrine very well, unfortunately Watchtower doctrine is quite simple and where it deviates from mainstream Christianity is usually wrong.
A simple look at the history shows why. Russell had no great religious knowledge, yet started a new religion by pasting together the bits he liked from other religions, something he admited to himself. When Russell died Rutherford discarded many of Russells teachings, calling many Satanic and introduced his own. This shows that Holy Spirit did not direct the religion, it was just the ideas of untrained men.
In general JW's are well intentioned, but it can be a dangerous religion. Extreme reliance on rules, the hypocritical stand on blood, and the extremely damaging using of disfellowshipping makes being a JW potentially damaging to a person in the long term.
I have posted some of the changes and some of the inaccuracies that i found with a little bit of research at www.jwfacts.com