What is the ruling on one who refuses to lead the prayer, despite fulfilling the conditions and there being no one equal to him, or there being someone of lesser standing than him?

It is permissible for someone who meets the conditions of imamate to decline it if he finds someone whose imamate is valid, even if that person is less حافظ (memorized in Quran) or learned than him. However, if no one suitable for imamate is found, then it becomes obligatory upon him.