In the name of God
For this discussion I try to go head step by step. First of all, we should see that we need a government or not. then we discussed we need what kind of it for our societies or for all the world.
According to Ayah 30 Shorah Rom the need to the government is the
basic and important need for human beings for ever and in every
places. In a hadith of the Prophet (p) we see that he (p) said that
if you are three, one of you must be a leader of the group. Ali (p)
also insisted that all the societies need government.
Addition to that two sources we see that some scholars try to prove
the neccesity of it by some reasonable evidences:
1- Islam is the religion for all the world, so for gaining this goal, it needs the complete structure. Also because of it one of the prophet's station is the sanctity of the people in particular Muslims (Ayah 6 Shorah Ahzab).
2- The continues of Islam as a religion to Al-Qiyama (Day of Resurrection): the emergency of it and also Ayah 144 Surah Al-Emeran shows that all the prophet’s status must be protected, So for this point the prophet (p) should have the successor. Also the determination of the successor is like the prophet-hood according to Ayah 67 Surah Maedeh and according to ayah 3 surah Maedeh is the preference of the religion (Islam).
3- The preference of the Shariah (Islam).
we know that if all the sects of Islamic jurisprudence agree with the
necessity of the existence of the successors, they have different
ideas about the applicability or referent of it. Shia believe in Imamate of Ali (p) and his Sons, but Sunni believe in Abu-baker and O'mar and O'sman and also after them, O'mavi's kingdom. Also we see some differences in this topic between them. The way of choosing the successors. Shia believe that the prophet determine Ali (p) as the successor in Ghadir according Ghadir Hadith. But Sunni believe that the Muslims (Ijima) must determine the successors so they went to Saghifeh and decided to choose Abu-Baker but after that Abu-baker himself choose O'mar as the successors of himself (1).
In response to the second question
we must know that the Imamate (in Shia belief) and the caliphate (in
Sunni's idea) is not only the government of Islamic countries. It
means the government for all the world according to idea of Maverdi
(Shafie's Scholar) and Fakher-al-Mohagheghin (Shia's scholar).
Another important point is that although Shia and Sunni don't have the
same idea about the way of determining the successors, they believe
that the origin of prophet's political authority is Divine or from
God. So according this point and according to the need of people to the divine's guidance the necessary stipulation or condition of political authority over Islamic societies is legality or legitimization from God. So following any orders from others except God is following the oppressor or the evil-doer according to ayah 60 Surah Nisa.But another important point is efficiency of the government is depended on the people's protection of the government. So legality of it is dependent to people and the sovereignty of the oppressor according to Islamic Law is not accepted except in idea's of some the Sunni scholars. According idea's of Ali (p) the sovereignty is impossible when people don't protect the government.
Shia scholars in particular Imam Khomeini have good reasons for their Idea of the guardianship of the jurisconsult or the government of the jurist in the absent of Imam Zaman (p). They believe that two factors are necessary for governing: God and people (2).
So by review of these ideas we can decide which one of form that are told in the Question is OK or suitable for Islamic Societies.
1- It is an additional explanation that clear some points: Before the death of prophet (p) all the orders of God had been received by the prophet (p), but after the death of the prophet most of Muslims thought that the receiving the orders from God Stopped so they tried to find the new Source.
This point of view in choosing Abu-Baker for Caliphate became more
strong among Sunnis because for this matter there is no source in Quran and Sunnah. But for imamate of Imam Ali (p) we have hadith Ghadir which you can find it in Sunni and Shia traditions. So Ijima of
Muslims became the source of Islamic Law.
In Shia view the subject is very different because Ijima doesn't have the same meaning of the Sunni's because Sunnis define it as all of view point of all Muslims. but we don't have any Ayah or hadith that the ideas of Muslims is evident or considerable.
Also it become the source after the short absence of Imam Zaman (p)
and when it is evident that it discover the view of the prophet (p) or
So in Sunni traditions Ijima is the independent source but in Shia
view is the dependent source that is relevant to the perspective of the
prophet (p) and Imam (p).
2- I want to explain about the reasons of their Idea of the guardianship of the jurisconsult or the government of the jurist in the absent of Imam Zaman (p) here:
In Shia belief Sunnah as one of sources in Islamic jurisprudence is combined from two part the Sunnah of prophet (p) and Sunnah of Imams (p), So they have two Sunnah from two Imams that prove their Idea of the guardianship of the jurisconsult or the government of the jurist in the absent of Imam Zaman (p):
A- A hadith from Imam Zaman (p) in which he (p) said that
وَ اَمَّا الحَوادِثُ الوَاقِعَهِ فَارجِعُوا فِیهَا اِلَی رُواة
حَدِیثِنَا فَاِنَّهُم حُجَّتِی عَلَیکُم وَ انَا حُجَّة اللهِ عَلَیهِم
in the events you should refer to the narrators of our hadith and
they are the ruler and arbitrator for you and I am the divine proof
If we understand the meanings of "event" and "the narrators of our hadith" we can understand that Shia scholars how prove this theory of Islamic government.
-"event" isn't mean the legal ruling because the word "event" has big meaning that refer to the event of Imam Zaman's absence era. If it refer to the legal meaning it must be mentioned in question but it is not mentioned.
-"the narrators of our hadith" doesn't mean the persons narrate their hadith but it means someone who know the tradition supported by a chain of transmitters going back to the prophet in an uninterrupted manner because if they don't know the genuine tradition, may be calumniate or slander the prophet (p) or Imams (p).
B- A hadith from Imam Sadeq (p): Before I explain it I should say that many of Sunni scholars like Abu-Hannifeh, malek Ibn Anas were the student of Imam Sadeq (p) and also Shafie was student of Imam's sadeq's (p) daughter in law in Egypt. So I think if new sunni scholars believe in Abu-Hannifeh, malek Ibn Anas and Shafie, they should accept Imam Sadeq's (p) courses in Islamic Jurisprudence.
In this hadith he (p) said that
«…مَن کَانَ مِنکُم قَد رَوَی حِدَیثَنَا وَ نَظَرَ فِی حَلاَلِنَا وَ
حَرَامِنَا وَ عَرَفَ اَحکَامَنَا فَلیَرضَوا بَهَ حَکَماً فَاِنّیَّ قد
جَعَلُتهُ عَلَیکُم حَاکِماً فَِاذاَ حَکَمَ بِحُکمِنَا فَلَم یَقبَلهَ
مِنهُ فَاِنَّماَ اِستَخَفَّ بِحُکمِ اللهِ وَ عَلَینَا رَدَّ وَ
الرَّادُّ عَلَینَا کَالرَّادِّ عَلَی اللهِ وَ هُوَ عَلَی حَدِّ
If someone know our hadith and our legal ruling you should refer to him and he is the ruler and arbitrator for you and if someone don't accept his judge he disobey us which is like disobedience of God.
There is no doubt that this hadiths refer to the jurisprudent or Shia jurist who govern the Islamic republic of Iran not Saffavih governor because the Saffavih governor were kingdoms who didn't have any Knowledge about Islamic jurisprudence.
The last point is that Shia scholars have some other reasons for their idea which called the reasonable evidence. These reasons are also emphasize that by help of wisdom we can prove vellayat faghih.