Which of the two mosques offers a greater reward for prayer: the one frequented by a larger number of worshippers and that has a specialized shaykh, or the one with fewer worshippers and no shaykh? And is it permissible to leave the more crowded mosque to go to the less crowded one with the intention of supporting it?

It is better for a Muslim to pray in the mosque with the largest congregation, to increase the reward for prayer therein. It was narrated from the Prophet, peace and blessings be upon him, that "A man's prayer with another man is purer than his praying alone, and a man's prayer with two men is purer than his praying with one man, and the more numerous they are, the more beloved it is to Allah, the Almighty, the All-Glorious." However, if the other mosque does not hold a congregation except with the presence of the worshiper, then praying in it is better and more preferable, in order to revive the congregational prayer in that mosque. Based on this, it is preferable to pray in the mosque with the largest congregation, while it is permissible to pray in other mosques.