What exactly makes Christianity the true religion and all the rest just wrong?

I have asked some christians why they believe, and some have said they know their religion is the right one for them because they have seen the way Christianity has changed the lives of people they knew, or has changed their own lives. I guess that's proof enough for them. I mean come on, you gotta believe in something, right? But you also have to be torerant of other faiths.