Praise be to Allah.
Many saheeh ahadith have been narrated which explain to the Muslims who is most qualified and has the most right to lead the prayers. One of these ahadith is that which was narrated from Abu Saeed al-Khudri (may Allah be pleased with him), who said that the Prophet (peace and blessings of Allah be upon him) said:
If there are three people, let one of them lead the others in prayer, and the one who has the most right to lead them is the one who knows more Quran.
(Narrated by Muslim, no. 1077).
The Messenger of Allah (peace and blessings of Allah be upon him) said:
The people should be led in prayer by the one who has most knowledge of the Quran and has been reciting it for longer. If they are equal in their knowledge and reading of the Quran, then they should be led by the one who made hijrah first. If they are equal with regard to hijrah, then they should be led by the one who is older
(Narrated by Muslim, 1079).
To sum up what is indicated by these ahadith, the one who has the most right to lead the others in prayer is: the one who has most knowledge of the Book of Allah and of the fiqh of salah.
Those who knew more of the Book of Allah were appointed to lead the prayers at the time of the Sahaabah, because they had learned the correct way of reciting the aayat and they had learned the knowledge contained therein and the deeds prescribed by the Quran. So they combined knowledge and action [they acted upon what they had learned], and did not stop at merely memorizing as is the case nowadays. How many people learn all or part of the Quran, take care to recite it properly and with a beautiful voice, but they do not know anything about the fiqh of salah.
If they are equal with regard to knowledge of the Quran, then the one who knows more about the Sunnah should lead the prayer. If they are equal with regard to knowledge of the Sunnah, then the one who made hijrah first should lead the prayer. If they are equal with regard to hijrah, or if this does not apply, then the one who is older should lead the prayer, as is indicated in the hadeeth of Maalik ibn al-Huwayrith, who said:
We came to the Prophet (peace and blessings of Allah be upon him), and we were young people, close in age. We stayed with him for twenty days, and the Messenger of Allah (peace and blessings of Allah be upon him) was kind to us. When he thought that we were missing our families, he asked us about those whom we had left behind, and we told him. He said, Go back to your families and stay with them. Teach them and instruct them and he said some things I remembered and some that I forgot. And pray as you have seen me praying. When the time for prayer comes, let one of you call the Adhaan and let the oldest among you lead the prayer.
(Narrated by al-Bukhaari, no. 6705). If they are equal with regard to recitation of the Quran, knowledge and hijrah, the Prophet (peace and blessings of Allah be upon him) commanded that the eldest of them should be appointed to lead the prayer. If they are equal in age, then the one who is most righteous (has most taqwaa) should be appointed, because Allah says (interpretation of the meaning):
Verily, the most honourable of you with Allah is that (believer) who has al-Taqwaa (is one of the pious) [al-Hujuraat 49:13]. If they are equal in all regards, then they should draw lots, if there is a dispute.
Having a PhD or having lived the longest in the land of the kuffaar does not qualify a person to lead the prayers. The one who has memorized more Quran and has more knowledge of the fiqh of salah is the one who should be appointed. It is not right for Muslims to dispute over the leadership of the prayers on the basis of their personal whims and desires. They should appoint the person who is described by shareeah as being qualified to lead the prayers. We ask Allah to reform the Muslims.