Having grown up in a non-Christian home, and having done a decent amount of work in Christian apologetics and having spoken to many people of all sorts of backgrounds, from atheists, agnostics, materialists, communists, etc., the evidence for the Bible is irrefutable and incredibly powerful. (For example, see the evidence here and here.) The Bible contains vast numbers of specific and detailed predictive prophecies that cannot be explained away. Many other categories of evidence, from incredible scientific facts, to pinpoint archeological accuracy, etc. validate the Bible (and, of course, it is self-attesting and self-authenticating as God's Word; "never man spake like this Man," Jn 7, etc.) I have never spoken to an atheist, agnostic, or other skeptic. who has what approaches anything like a decent explanation for the predictive prophecies and other categories of evidence for the Bible. When I speak to people like that, I never go away saying, "Boy, I wonder if the Bible is really true--they have such great stuff against it!" On the contrary, it is always, "Wow, how incredible God's Word is--it's too bad, because of his sin, he isn't willing to listen to the evidence for it and makes up such foolish reasons to reject it!"
Now let's contrast that with the writings of Ellen G. White, founding prophetess of the Seventh-day Adventist denomination. Even looking at the most voceiferous defenders of her writings, there is nothing in them that is like the specific predictive prophecies and other categories of evidence for the Bible. Even if one were to set aside the plain false prophecies in her writings (see here) as the inventions of evil people who have some kind of irrational hatred of the SDA movement, there simply is nothing comparable in what she wrote to the evidence for Scripture. Christian apologists regularly debate skeptics on college campuses and in other places and crush them with the intellectual power of the Bible, but I can't imagine a Seventh-day Adventist even trying to do that with Ellen White's writings against an equally intelligent and well-researched opponent.
Now let's compare the size of the Bible and Ellen White's writings. A typical Bible has around 1,000 pages, but EGW's writings are around 100,000 pages, according the White Estate. How reasonable is it that only 1% of God's revelation, the Bible, is attested in such an incredible way, by apostles, etc. who raised the dead, reattached missing limbs, and so on, but 99% of God's revelation, EGW's writings, were composed by one person who did no apostolic miracles (and admitted she couldn't), and whose writings simply have nothing like the overwhelming evidence for them that the Bible has?
Even apart from other facts, like the fact that 99%+ of the Bible was written by holy men, not by women (because men are to lead/have authority), the striking difference between 66 books in Scripture and only one lady writing 99 times as much as all the other inspired authors combined--Ellen White's writings do not meet the standard for something that is the Word of God. There is no proof of their inspiration at all.
The same sort of argument is valid for the allegedly inspired books of Mormonism, the Christian Science cult of Mary Baker Eddy, the Koran, and all other books that claim to be inspired outside the Bible--including the Apocrypha. Even apart from the way that they contradict Scripture and are filled with factual errors--the negative disproof of them as God's Word--there is no positive proof for any of them. Only the true God can bring about the predictive prophecies found in the Bible (Isaiah 44)-- that is why no other book claiming inspiration has anything like them.
Readers who think that something outside of the Bible is inspired ought to consider these facts and reject their nonbiblical books. They can get further help here. Christians can use the facts above to help unconverted cultists consider their ways.
By the way, if you are a Ruckmanite who believes that the King James Version was produced in 1611 by the miraculous inspiration of the Holy Spirit the way that the original manuscripts were, you need to consider what evidence there is for your view also. Could you win a debate with an atheist on a college campus with the alleged evidences for the miraculous giving of the King James Version by the Holy Spirit in 1611? As readers of this blog know, I am passionately KJVO, with a knee-jerk reaction to defend the translation of the King James whenever it is criticized, am totally committed to the perfect preservation of Scripture in the Old Testament and New Testament's Textus Receptus, etc. (see here), but you can't defend with Scriptural exegesis a move from the Holy Spirit in 1611 like that which took place in the production of the original manuscripts of the Bible, so if you are going to take that view, you are going to have to do better than the weird and totally unconvincing things that people like Gail Riplinger make up to support it.