"Are JWs Christian" is an argument that is best not used when trying to prove the JWs are not the one true religion.
The definition of being "Christian" is different things to different people.
In the simplest of terms, JWs are Christian in that they believe in Jesus as God's son, they accept him as their savior and pray through him to God. Ask a JW if he's a Christian and he will reply that he is.
But at the same time, if you dig deep enough into their own theology, there is evidence to imply that the non-anointed members are not Christians. Jesus is mediator only for the 144,000. Only the 144,000 make up the true Christian congregation. The non-anoined are often times called "companions" to the true Christians.
They contradict themselves so much on the issue that either side of the arguement can present enough printed material from the WTS to prove their side of the argument. I think the Society does this on purpose. They want outsiders to think of the religion as "Christian" and they confuse the average member into thinking that all members are Christian which helps bolster the idea that the entire religion is Christian, but when broken down to the nth degree, one has to question if the JW doctrine really allows for the non-anointed to be Christians as defined in their own literature...not what the majority of outsiders consider Christian.
This is an interesting illustration:
To put it another way, imagine that Coca Cola, Pepsi, and Schweppes decided that some generic brand of cola isn't really cola because it happens to be less similar than the big corporation colas are to each other. It would be invalid, because it is not the position of those groups to determine what falls within the defintion of cola even if the generic cola is an inferior product.
Where I come from most people call any soda a "coke". If they order in a diner, they'll say "gimme a coke", meaning whatever soda is available. In that sense, all sodas are "coke"...but not all sodas are "Coca-cola" or "Coke". Similarly, in the general sense of the word, as most people consider it, JWs are Christian. But in their own doctrine, there is a question as to if the non-anointed are Christian or not. So you could say that all JWs are "coke", they're just not all "Coca-cola".