If God is all powerful,there can only be one God since there cannot be two "most powerful" beings. Any religion that affirms multiple gods really views their gods as less than what what God is by definition, all-powerful. I choose the God who does not have to share His power with another. Why choose a lesser power or risk choosing a God who might have the potential of being defeated?
The famous athiest, Bertrand Russell, wrote in his "Why I am not a Christian," that all religions cannot be true since they affirm different things. Since two opposing truths cant both be true, there must be only one true religion and all others must be false. Christianity says that there is only one true religion. Any religion that affirms many possible true religions must be wrong.
Christianity is different from all other world religions in that all other religions require the individual to be saved by his/her own good works. In Christianity, one is saved by Christ's righteousness given as a gift when one chooses to rely on His gift by faith. If there can be only one true religion, and since all other religions are "saved by works" religions, the one that is distinct, Christianity, must be the true one.