What is the ruling on preferring one Companion over another?

Love for the Companions is faith and belief, and hatred for them is disbelief and hypocrisy. They vary in merit. The best of them are the Four Caliphs, then the remaining ten promised Paradise, then the people of Badr, then the people of the Pledge of Ridwan, then those who embraced Islam early before the Conquest, then the Muhajirun (Emigrants), then the Ansar (Helpers), then the rest of the Companions. Abu Sa'id al-Khudri, may Allah be pleased with him, was a noble Companion and the Mufti of Medina. He witnessed the Battle of the Trench and the Pledge of Ridwan. All Companions must be loved, but one should not believe in Abu Sa'id's superiority over the Rightly Guided Caliphs and the Ten. It is advised to study the biographies and virtues of the Companions, especially the biographies and merits of the Rightly Guided Caliphs, and to strive to make one's love conform to what is enjoined by the Sharia and the Sunnah.