One thing I will say is that the JWs as individuals are generally good people, so there's no point in being rude or confrontational with them. In fact, you shouldn't even try to argue that they're wrong, as no Witness will really listen to your argument anyway.
If anything, you should have compassion. There are older JWs who have spent decades door knocking, thinking that they would never die, and live in a perfect world. There are poorly adjusted uneducated young JWs who were indoctrinated at an early age and, if baptized, risk losing their family and friends if they stop. For the most part, they are victims, not villains.