Just for background, I DA'd 12 years ago and I'm now an atheist/agnostic.
I normally avoid answering to the JWs (I can usually tell it's them because I hear two sets of incredibly moving footsteps coming up the stairs to my flat) or they do a quick "magazine presentation" and then they're off. On one occasion a few weeks ago I answered and the guy seemed up for a discussion. I said I was an atheist, a lengthy discussion ensued and he "placed" a creation /evolution leaflet with me.
I was expecting a call and, after avoiding them a few times, I finally answered. We went over much the same ground again and today he came back for a third visit.
Most of this time the discussion is on the creation argument. It's tempting to bring up something like 1914 or 607 but that would be a giveaway. I asked him today how long he believed humans had been around. I was surprised that he said 6000 years as I had suspicions the WTS had backtracked on this were keeping the length of the Genesis "day" vague in light of the indisputable scientific evidence. We also got on to the flood and I again said that flies completely in the face of everything science knows.
I said a few times that he needed to look outside of what his literature (and the carefully selected scientific quotes therein) said to look at what science in general thought. Of course, he said they did all the time, which was rubbish - at least they're not looking in the right place. He did close by saying he was going to go away and look at the "secular view" on the flood and the 6000 years.
It's not as if I think I have much chance of planting seeds of doubt in his head, but I guess I find the discussions interesting - although less and less so with each visit. It's interesting to be on the other side of the fence from where I was. Mind you, if I were the pioneer, I'd have given up on me by now!
I guess if I get bored with the discussions, I'll just bring up 607 and I won't see them again.