Jesus at one point claimed to be "the way, the truth, and the life". Jesus was not making claims about one religion being better than all the other religions. That completely misses the point, the depth, and the truth. Rather, he was telling those who were following him that his way is the way to the depth of reality.
Rob Bell, Velvet Elvis, p. 21
14:1 Let not your heart be troubled: ye believe in God, believe also in me.
14:2 In my Father's house are many mansions: if [it were] not [so], I would have told you. I go to prepare a place for you.
14:3 And if I go and prepare a place for you, I will come again, and receive you unto myself; that where I am, [there] ye may be also.
14:4 And whither I go ye know, and the way ye know.
14:5 Thomas saith unto him, Lord, we know not whither thou goest; and how can we know the way?
14:6 Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me.
So, let's see...
Jesus is talking about going away to prepare a place for the disciples, but returning for them and us so they can be where He is. Thomas basically says he doesn't understand, but Jesus explains that He is the way, and that no one comes to the Father except through Him.
In saying He's going away, Jesus is talking either about His death or more likely about His ascension. His words about coming again are much the same as the angels' at His ascension, "this same Jesus...shall come in the same manner as He has gone into Heaven".
In other words, Jesus tells this to His disciples, giving them hope concerning the things they were to soon experience.
Bell clouds the issue somewhat, by making it about religions. It's may not be about any religion that calls itself Christianity (as Mormons may try to sell themselves), but it is about people being true Christians.
Perhaps a better question than who's right, is who's living rightly.
No, it's about believing in Christ, which does have to do with who's right. The Pharisees, Sadducees, Scribes, all would have said they were living rightly. In a sense, it wasn't their attempts at moral living that were wrong, it was that they didn't know Him when He came.
As Paul says, in Romans 9
10:1 Brethren, my heart's desire and prayer to God for Israel is, that they might be saved.
10:2 For I bear them record that they have a zeal of God, but not according to knowledge.
10:3 For they being ignorant of God's righteousness, and going about to establish their own righteousness, have not submitted themselves unto the righteousness of God.
Strange, that Bell says it's not about being right, but Paul says that his people's problem wasn't their zeal for God, but that they didn't have or didn't exercise the knowledge they needed for the zeal to be good. Paul as Saul was zealous, but he was wrong, so it's likely he knew a bit of what he was talking about.
The question is still "Who's right", because it's only when that question is answered that one can determine who's living rightly. It make the question "Who's living rightly" presupposes that one has already determined what are the standards for 'living rightly', that one's standards are in fact the right ones, or to put most plains, that one is right.