Sahaba
Regarding the other parts of chain of narration, all people are up to be scrutinized. There is no distinction made between a Sahaba and a taba'een or anyone else regarding trustworthiness, everyone have the same demand to prove or disprove their trustworthiness. Therefore, Shia look at each Sahaba as an individual, preferring some above others.
Shia do not have a ranking system dependent on when the Sahabi embraced Islam, because they argue that this does not matter for one's faith at all. Rather, they have an individual view of each one, according to what they did during their life. For example, if a Sahaba made Muhammad angry or questioned his decision several times then he is viewed as unrealiable. Furthermore a Sahaba who engaged in open warfare against the Ahl al-Bayt have their trustworthiness reduced to near nothing in the Shia view. In fact, under the doctrine of Tabarra, it is obligatory to disassociate from such a person.
Shias consider that any hadith where Muhammad is claimed to have, in one way or another, absolved all Sahaba from sin or elevated their trustworthiness is false. Shias claim that, in most cases, such hadiths have been reported by those who opposed the Ahl al-Bayt.
On the other hand, the Sahaba that are agreed to have sacrificed life and property for the sake of Muhammad are held in a very positive view, and under the doctrine of Tawalla, it is obligatory to love such a person.
Read more about this topic: Shi'a View Of The Sahaba