This is a bit broad, but in general the Roman Catholics speak of two sources of authority: Scripture *and* Tradition (or in some formulations, Scripture, Tradition, and Reason.)
We Orthodox tend to speak of one source of authority -- and that is Holy Tradition. Ultimately, Holy Tradition is the living existence of the Holy Spirit in the Church. It is expressed and conveyed in various documents and oral traditions, but those documents and oral traditions are not Holy Tradition itself.
Within the documents and oral traditions that convey Holy Tradition, we see a continuum of reliability and authority. Scripture is at the pinnacle of reliability those documents of the Church that convey the revelation of God to man. But even within Scripture, there is a hierarchy of sorts, as one can tell by how it is read and interpreted and by how it is read liturgically. Highest is the four-fold Gospel, then the rest of the New Testament and the book of Psalms. Within the Old Testament, the books of Isaiah, Proverbs, Genesis, and Exodus are given particular pre-eminence, and certain passages are of very high importance (I especially think of the 8 Old Testament Biblical Canticles traditionally sung at Matins). The deuterocanonical books are not as important as the Old Testament proper.
After this come the declarations of the Ecumenical Councils, then the liturgical texts, writings of the Fathers (also with a hierarchy of importance and reliability), etc., etc. All of these things must be interpreted in light of Scripture, but at the same time, it is the Church that has the ability and authority to interpret Scripture -- this is part of the great importance of the liturgical texts, writings of the Fathers, etc.
Read the first section of Bp. Kallistos (Ware)'s book if you want to understand more. The section on Holy Tradition is short, easy to read, and one of the best expositions I have seen. I posted it sometime last year, and we had a good discussion.
http://www.fatheralexander.org/booklets/english/history_timothy_ware_2.htm
I didn't realize you believe there is a sort of hierarchy within scripture, thanks for pointing that out and for your answer. If you'd like to see the Catholic view of authority, Jo gave it to me in his 3053 including comments on Tradition. My answer is in 3170. If you read them you will see that I'm struggling with how to see infallibility within the context of Tradition.
Even here, you said that Holy Tradition was authority. I have been told that the Protoevangelion is part of Holy Tradition. I have also been told that it is not infallible and it is not authority, although it contains elements of truth. I don't know, I'm starting to think that maybe my mind is in some kind of a mental rut that I can't seem to shake, that the answer is easier than I'm making it, but I'm just so focused down one path of thinking that I can't see it. :)
Thank you for the link. I will take a look at it.