Yes, Christianity is the one true religion. That may sound awfully dogmatic and narrow-minded, but the simple truth is that Christianity is the only true religion. Jesus said that He alone was the way to the Father (John 14:6), that He alone revealed the Father (Matt. 11:27; Luke 10:22). Christians do not go around saying Christianity is the only way because they are arrogant, narrow-minded, stupid, and judgmental. They do so because they believe what Jesus said. They believe in Jesus, who claimed to be God (John 8:58; Exodus 3:14), who forgave sins (Mark 2:5; Luke 5:20; 7:48), and who rose from the dead (Luke 24:24-29; John 2:19f). Jesus said that He was the only way. Jesus is unique. He was either telling the truth, He was crazy, or He was a liar. But since everyone agrees that Jesus was a good man, how then could He be both good and crazy, or good and a liar? He had to be telling the truth. He is the only way.
Christianity is not just a religion; it is a relationship with God. It is a trusting in Jesus and what He did on the cross (1 Cor. 15:1-4), not on what you can do for yourself (Ephesians 2:8-9).
Buddha didn't rise from the dead, nor did Confucius or Zoroaster. Muhammad didn't fulfill detailed prophecy. Alexander the Great didn't raise the dead or heal the sick. And though there is far less reliable information written about them, people believed in them.
The scripture is right when it says in 1 Pet. 2:7-8, "This precious value, then, is for you who believe. But for those who disbelieve, 'The stone which the builders rejected, this became the very corner stone,' and, 'A stone of stumbling and a rock of offense'; for they stumble because they are disobedient to the word, and to this doom they were also appointed."