The greatest rift is between the supporter and anti wilayet e faqih marjas.
Wilayet e faqih is a concept invented by usoolis to govern in the absence of 12th.There is no Shia hadith that supports such a wilayet in ghayabah.But to oppose this is dangerous. A personality that is well known in shiat because he was the brother of sistani, was killed by Iran because he was against wilayet e faqih.
http://www.yahosein.net/vb/showthread.php?t= According to the students of Mahmud Sistani. Khamene'i had him poisoned
The rift started early with the arrest of ayatollah montazeri, the successor of Khomeini and o prominent scholar. It is a well kept secret in Qom that he was arrested because he wrote that Fatima had no right on property of fadak.
https://youtu.be/9aj_ZK7YxnE
Ayatollah Shirazi who was a strong opponent of wilayet e faqih was dealt more severely. He was assassinated and secret service people stole his corpse!
Ayatollah najfi dhakoo is severely criticized by other marjas, for his stand against certain bidet in azadari and shadat e salsa.
Most marjas have given fatwa against Ayatullah fadhullah, because he gave a fatwa against abusing the sahaba.
And kamal hyderi criticized every marja in show Mutarahat fil-'Aqeedah.In it he claims that Sistani has no knowledge and only political leverage. Although shias have removed the video, but the foolishly placed a refutation, which proves the rift between the marjas.]
https://www.youtube.com/watch?v=fZj215wwm7U