Is Christianity the one true religion?

Yes, the Bible teaches that Christianity is the one 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 believe he was the Son of 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).
Buddha didn't rise from the dead, nor did Confucius. Muhammad didn't fulfill detailed prophecy. There is far less reliable information written about them, yet they are believed in.