The New Testament alone has over 20,000 ancient manuscripts that date to within 150 years of the originals (50 if you include a fragment of the Gospel of John) that attest to its historical reliability. In other words we can take what we have today and compare it to manuscript copies that were written by third generation Christians. The chances of the text being corrupted within that time span are zero. Not to mention that if you compare all of the copies with each other, they are 99.5% similar. The majority of the differences are in spelling and grammar. Of the 20,000 lines that make up the New Testament, only 40 are disputed by scholars (none of which jeopardize any orthodox Christian doctrine).
Compare that to the manuscript evidence that the Book of Mormon boasts...zero. The only known manuscript, the Golden Plates, were never seen by the general public and only attested to by a scant few individuals, some of whose pasts are pretty sketchy. To add to that, they were returned to an angel and are now inaccessible according to Mormon theologians. Hmmmmm... Why would God do that? He provides endless evidence for one of His holy books, but the other, which is the "fullness of the Gospel," He provides nothing but the testimony of one guy whom He hopes we'll all believe (and what in the world is "reformed Egyptian"?).
So to put this in perspective, one book has more evidence than any other book of antiquity ever; the other has absolutely no evidence that it ever existed until 1830.
This is an honest inquiry. I have no desire to attack or make any of my friends who use this book angry. I enjoy thinking and I want to encourage others to think as well. Subject your beliefs to scrutiny. I have done so with mine and am more convinced than ever that the Bible is God's word and is sufficient for what we need to know to be saved, that Christ is God who became man to die for our sins, and that He sent the person of the Holy Spirit to dwell with His people.
A good book to check out about the reliability of Christianity is Josh McDowell's New Evidence that Demands a Verdict. Check it out.