It's not the best or most important verse in Quran per Mohammad (s), it's the verse of climax. And the only reason it's that climax is the foundation of how the Quran starts in Suratal Baqara, and flows to that apex. You get to an emotional high in Quran at that verse and you can't get higher if you recite Quran then that peak if you recite properly through the help from the spirit from God.
That said, if you read Suratal Baqara often, this verse when recalled, you kind of recalling the whole feeling to getting to that, and then the climb down in the Surah. The peak emotion itself when recalled, is highly boosting energy wise and can remove attempts of fear, sorrow, and depression by dark forces on a human. It can also due to the nature of the topics to that peak, be a way to protect or remove dark magic and knots blown upon.
The foundation of that apex is "those who believe in the hidden". Ayatul Kursi is an emotional climax, but to be honest, is not a revealing and important as other verses like 42:23. 5:12 and 4:59 which the guidance of all humanity is dependent upon.
The climax here is just an expression of what 40 other verses say, that to God belongs the authority of the heavens and earth. It's just where it is, and the way it's said, and the connection of Al-Hayu with the topics before, it's a climax. You can say it's this verse that the 40 mulk verses in Quran get boosted as well by it, and they are given more light and life so to speak by this verse as well.
As you know religion of God has been titled among many titles as submission, here it's saying, that God's seat extends over the whole of existence and this the authority of God given to Talut (a) as well to all his chosen ones and these are those that intercede by God's permission.
There is no most important verse in the Quran however. Guidance wise the peak is the verse talking about Mohammad (s) connecting through a ladder to heavens or opening in the earth if he can to bring a sign and proof that would make them see and believe beyond doubt, but showing it's not even possible, for him to do so because of their oppressive stubborn state of rebellion, disquiet doubt, running away from God and disbelief. And this also has other foundations else where with the talk about doors to sky and the stars of guidance in the sky that is a refuge and safeguard from every devil.
Those verses are the peak of guidance, but then there is so many topics and doors to doors, what was once not a significant verse because significant.
Politics wise - the Mahdi - is the greatest warning in Quran, and the verses warning about destructions of cities, are important. For social push and for us to help God and try to prevent the worse case scenarios Quran warns about in the end of times, we need to believe in these verses.
So if you need to make the journey, there is other verses more important. But once you make the journey and trying to guide others, other verses become more important to you.
And if you need to ascend, some verses more important. If you don't see Ahlulbayt in Quran, there is plenty of verses that are mort important in this regard for you to pay attention to till you witness them in Quran repeated through out it's pages.
What I'm trying to say, is there is no most important verse. What verse is most important depends on your stage.
