When the two young men show up at your door, most will not make a presentation like the one that follows. Nevertheless, for someone wanting to see some of the differences between Christianity and Mormonism (particularly with respect to the Gospel and the afterlife), the following blog entry from Mormon Matters provides some succinct distinctions.
Obviously, I do not endorse Mormonism. Nevertheless, the article may be eye-opening if the only thing you know about Mormonism is that they wear special underwear. (link)
It is key to be aware of the fact that we teach a very different gospel from Mormonism. We teach the pure gospel taught by Jesus and the apostles.