I can't understand how Sahaabah are the best of the ummah

Sahaabah killed eachother. Killed their leaders. There were many who left islam and refused to give Zakat after prophet died. The thing with Mu'awiya and Ali. Many of them became muslim after muslims gain power.

I just can't understand how they are the best of ummah aren't there much better muslims who are not companions.

Are companions just better than them because they see probhet with their own eyes?