As a few have pointed out debating doctrine with a JW is rarely effective because doctrine is always a matter of interpretation. However, this doesn't mean that their doctrine is always sound or firmly rooted in the Bible either.
In the process of waking up a few points really stuck out to me as follows;
*607/1914 - there is no indication in scripture that the prophecy in Daniel was to have any greater fulfillment than Nebuchadnezzar. The prophecy regarding "seventy years" (I believe in Jeremiah) was of servitude to Babylon and applied to all the nations around, not just Israel. The scriptures never come out and say it applied to the exile of the Jews. No scholar outside the WTBTS agrees with the 607 date for the fall of Jerusalem.
*Other Sheep/Great Crowd - there is no reason to assume any connection between these two terms in the Bible. Most scholars agree that the "other sheep" simply referred to the gentiles, not some nebulous group of people to be identified later. Furthermore, the idea that these two groups would have different hopes seems to contradict scripture ("One flock, one shepherd", "one hope"). All evidence seems to indicate that the The Great Crowd in Revelation IS in heaven (the temple sanctuary). Also, it only makes sense that the 144,000 would be symbolic considering everything else in that text is also symbolic.
*Faithful and Discreet Slave - There is no reason to believe this is anything more than a parable and is not prophetic. Not to mention this group would not be identified until after Jesus return, which if 1914 is wrong, would be impossible. If the FDS is a specifically identified group as the WTS tries to say than why isn't the evil slave the same?
*Governing Body - the term is not found in the Bible and neither does it ever explicitly show that one existed in the 1st century.
Most of these are addressed on sites like JWFacts. As with anything else they have to be weighed in a for/against fashion. If looked at from an outside, unbiased and critical way these doctrines do not stand up to scrutiny.