We are the only church that has the gift of the Holy Ghost. No other churches do. Period.
All people have the light of Christ available to them. That is the source of what light other people live by. Not only that, a great deal of the light and truth that we have as members is gained by the light of Christ. If you don't believe that, consider the ramifications of Joseph Smith's teachings:
"No man can receive the Holy Ghost without receiving revelations. The Holy Ghost is a revelator." (TPJS 328)
The consequences of that statement are plain. If we are not receiving revelations, we are not receiving the Holy Ghost. Now, certainly, there are revelations that are real revelations that we don't call revelation. For example, one way or another, members receive knowledge by revelation that the church is true. And sure, sometimes revelation comes like the turning on of a light switch, and sometimes revelations come like the dawning sun.
But there is a difference between discerning by the light of Christ and revelation through the Holy Ghost. All churches, in fact, all people, enjoy some measure of the light of Christ.
But the gift of the Holy Ghost is had only in the Church of Jesus Christ of Latter-day Saints. Other churches do not enjoy the Holy Ghost as part of their weekly services, nor do non members enjoy the Holy Ghost as part of their daily scripture study and prayer. Whatever they are able to enjoy through the light of Christ, we also enjoy.
But if we don't live beneath our privileges, a much greater gift has been made available to us, and to us alone. It is the gift of the Holy Ghost.