Luke 4:43: I must proclaim the good news of the kingdom of God to the other towns also, because that is why I was sent.
It appears that the good news is the kingdom of God made possible through jesus' sacrifice. So, both are right and arguing on stupid details.
Obviously, both agree to live by the principles common to Christians. Both believe in the forgiveness of sins through Jesus Christ. So, they have the basis there. And yet, they argue and call each other false teachers when rely... who cares!
If you call God "God", "Yahweh", "Jehovah", or "Jesus", how will that impact your faithfulness to your wife? And if you believe in Trinity or not, how will that change the love you give to your family and friends? And if you believe you will live on earth or in heaven, how will that change anything to you're idea that God will take care of you after your death?
What really matters in the end is what we do, our actions: these define who we are. We are not defined by what we believe or dream about. Its what we do! Yet, somehow, JWs and many other religions miss the point by arguing, calling other faiths all sorts of names and questioning their motives.