The resurrection of Jesus Christ probably is the thing that sets Christianity apart—because the other religions bring you a prophet or they bring you a sage, and they say: “This is the way to find God.” So in that sense they're all the same.
Christianity comes along and says: “This person IS God, and he was raised from the dead to prove it.”
And that is just a different category and you have to come to grips with that to be a Christian, and also it does force you in a way to grapple with it. Instead of saying: “I like this religion because it meets my needs” or: “I like these thoughts,” you have to say: “Did it happen or not?”
So I would say the resurrection would be the place to go. First you have to have the caviat that you can't prove anything—you can't prove that you're not a butterfly dreaming that you're a boy! You can’t prove that your cognitive faculties actually work—so at a certain point there's no such thing as absolute proof for anything.
But once you grant that, you move into where we normally go with: “How do you know things are true?” NT Wright wrote a book, The resurrection of the Son of God—890 pages of top flight historical research. What he basically shows in that book is not that you can prove anything from history (including the resurrection)—he admits that—but what he tries to show you is all alternate explanations for the data are even more difficult to believe.
He says if you don't have a presupposition that miracles are impossible, then it's very clear that the most likely explanation for:
is the resurrection. So he goes through in a very methodical way, and when you're all done you realise: if you don't rule out miracles before you start, then there's a very very powerful case for the resurrection.
So I'd suggest—not maybe at that level, you don't have to read 890 pages!—but there are other versions of that evidence that would be good to look at.
You might like to:
READ Mark’s Gospel (you can do that on this site, just click on “Read Mark”)
GET A COPY of The Case for Christ by Lee Strobel, a book which looks at the evidence for Jesus and asks all of the questions people have about who he was (you can get a copy here).