Who is the successor of the Prophet (pbuh&hf) !?

Once a person told me that Abu Bakr is more knowledgeable than Prophet Muhammad (pbuh&hf) (Na'oozo Billah)! I asked him how come?! He said because Abu Bakr understood that he should assign a person as his successor to keep the system and community working in order. as it is well-known Abu Bakr assigned Umar as his successor. But the Prophet failed to realize this important task that the Islamic community needs a qualified leader after him, or perhaps it was not important for the prophet that who is going to take over the power after him!

When I heard that, I started asking the following question from myself: Is it possible that the Prophet of Islam who has tried hard to implement Islam, and tolerated a lot of problems, disasters, and paid big price to establish Islam in Arabian peninsula, leaves people without assigning any person to keep this religion alive after him?! The religion that is to be the last religion of God for this world; the religion that was supposed to be for every nation all over the world both inwardly and outwardly (political authority). What happened that we Muslims are in this miserable situation in the world for centuries? What happened that the chain of successors/rulers (Ulul-Amr) has reached to people like King Fahd, King Husain, Saddam Husain, Husni Mubarak, ...? Something is terribly wrong!

Yes, The problem is leadership and Guardianship. Was this problem not so important for prophet or he didn't take it serious? Of course, he did take it serious and he must have assigned a chain of successors (Caliphs) who where the most qualified as the head of Islamic state and as the guardian of Shari'ah (divine law).

Another question that came out to my mind was that: Are Allah and His prophet more qualified to assign the Caliphs, or people? Is Islam on the basis of democracy (government of people over people) or on the basis of theocracy (Kingdom of Allah over the earth)? The history of Islam testifies that the government after the death of prophet was neither democratic nor theocratic. Just a few people gathered in "Saqifah bani Saaedah" and assigned Abu Bakr as Caliph while Imam Ali was busy of the burial of the holy prophet in Medina.

Is it our choice as to whom should be a Prophet or it is Allah's choice? Can we select Prophet by Shura? The same goes for assigning the successor of Prophet, for Allah knows best who is the most qualified for this position. It seems very strange that a deputy of a chief is assigned by any person other than him. Deputy of God (or prophet) is only assigned by God (or prophet), and it is not people's business! There are many examples in Quran where Allah states that He is the one who assigns a successor on the earth. Allah, Exalted He is, states in Quran:

"O' David, we assigned you as Caliph (successor) on the earth ..." Quran[38:26]

He also states:

"... We have assigned you (Abraham) as Imam (leader) for people ..." Quran[2:124]

as we see, Caliph/Imam for the mankind is assigned by Allah. See also [2:30] (about Adam). Even Prophet Moses, when he wanted to go to Miqaat, did not ask people to form a Shura to assign a Caliph for him. Quran tells us that:

(Moses said: "O' Allah) assign me a vizier from my family, (that is) my brother Aaron (Haroon) ...," (Allah) said: "We granted your
requests, O' Moses." Quran[20:29-36].

Allah, Exalted, also said:

"Surely We gave the book to Moses and assigned his brother Aaron as his vizier." Quran[25:35].

Allah also said:

"... And Moses said unto his brother Aaron: Take my place among the people." Quran[7:142].

Notice that "Ukhlufni" and "Khalifa" (Caliph) are exactly from the same root.

In this connection, let us take a look at the following interesting tradition in Sahih al-Bukhari:

The Messenger of Allah said to Ali: "Your position to me is like the position of Aaron (Haroon) to Moses, except that there shall be no Prophet after me"

Sunni References:
(1) Sahih al-Bukhari, Arabic-English version, Traditions 5.56, 5.700
(2) Sahih Muslim, Arabic, v4, pp 1870-71
(3) Sunan Ibn Majah, p12
(4) Musnad Ahmad Ibn Hanbal, v1, p174
(5) al-Khasa'is, by al-Nisa'i, pp 15-16
(6) Mushkil al-Athar, by al-Tahawi, v2, p309

The Prophet(pbuh&hf) thereby meant that as Moses had left behind Aaron to look after his people when he went to Miqaat (meeting Allah), in the same way he was leaving Ali behind to look after the affairs of Islam after he met Allah(i.e., his death). Let this reminder be food of thought for the possessors of pure heart and open mind.

The above verses of Quran concerning Aaron show that even the prophet does not assign his deputy/successor, and it is rather Allah who does that. Prophet Moses prayed to Allah and requested that Aaron becomes his deputy, and Allah approved the suggestion/request of Prophet Moses(as).