Which of the four schools of thought is the soundest, and what is the saved sect mentioned in the Hadith, "My Ummah will split into seventy-three sects, all of them in the Fire except one," along with mentioning the Quranic proofs?

Blind fanaticism that leads to hating and misguiding Muslims is forbidden. All Muslim imams are on guidance. The saved sect is everyone who follows the methodology of the Prophet, peace and blessings be upon him, and his companions. It is not limited to a specific group or country, but rather it is a methodology. This group may be dispersed throughout the earth and includes different types of believers.