I've had occasional chats with the Mormons over the years - they send a new couple of missionaries every year from the USA. (Ironically they used to rent a house from a local brother). They are usually friendly , personable young men , if rather tense and limited - they tend to stick rigidly to their script.
I remember discussing and reading the portions of Isaiah from the King James bible that are quoted word for word in the Book of Mormon (supposedly written hundreds of years previously) and neither of them had ever heard of this discrepancy , couldn't think of any explanation and weren't interested in providing one. When I asked if there was any evidence secularly for the existence of the tribes in the Americas , they seemed completely apathetic. It tends to be quite difficult to get any meaningful discussion based on the bible , as they often admit that they don't really know much about it , and have an easy "get out" if they disagree with any scripture ("how do you know that it has been translated properly"). One Mormon told me that this was the first time he had actually opened a bible for months.
As another poster mentioned , due to the lack of virtually any common ground between JWs and Mormons , usually the topic turns to "field service" style experiences (watch out for the dog at 24 Acacia Avenue etc).