A key difference between Christianity and Catholicism is the emphasis on tradition. Whereas Christianity focuses mainly on the word of God, Catholicism presents a number of extra traditions, which it holds to be authoritative. So, which is more authoritative? Scripture, or tradition?
Defining terms
Before we ask which is more authoritative, we have to ask what tradition and scripture actually are? Let us begin with tradition.
In short, tradition is "something that is handed down" (1). Because of this, even scripture itself is necessarily a tradition. However, so are many other things. Many religions, people groups, and even people as individuals, have traditions. This actually disarms a common Catholic proof-text. In 2 Thessalonians 2:15, we read "Therefore, brethren, stand fast, and hold the traditions which ye have been taught, whether by word, or our epistle." (emphasis mine). Catholics erroneously assert that, since Paul says we must hold traditions, theirs is an open and shut case. Yet, it is necessary to distinguish between "tradition" and "Catholic tradition". In fact, there are other scriptures that are very critical of the use of tradition. The main dispute Jesus had with the Pharisees was their strong reliance upon man made tradition.
But in this verse, Paul is helpful to clarify "the traditions which ye have been taught, whether by word, or our epistle". This really matters. It tells us that the traditions Paul is talking about are the scriptures. Now, this is where the Catholic might point out "but it says whether by word, or our epistle". And that's true. However, there are three things to consider.
First, it defies common sense that the Apostles would teach one thing by word, and another by mouth. It also defies the explicit teachings of those Apostles. They referred to themselves as "stewards of the mysteries of God" (1 Corinthians 4:1), and when one of them did go off script (they were human, after all), first of all they would endure the firm, possibly public rebuke of their brethren (e.g. Galatians 2:14-21), and second of all, would warn the Church not to listen even to them if they tried to change the message (Galatians 1:8).
Second, this wasn't the attitude of the early Church. Irenaeus is an excellent example. Speaking of heretics, he wrote "When, however, they are confuted from the Scriptures, they turn round and accuse these same Scriptures, as if they were not correct, nor of authority, and [assert] that they are ambiguous, and that the truth cannot be extracted from them by those who are ignorant of tradition. For [they allege] that the truth was not delivered by means of written documents, but by word of mouth." (2).
Third, we know that what the Apostles wrote as epistles, they also sent out teachers to preach the same thing by word. In Acts 15:25-27, for example, we read "It seemed good unto us, being assembled with one accord, to send chosen men unto you with our beloved Barnabas and Paul, Men that have hazarded their lives for the name of our Lord Jesus Christ. We have sent therefore Judas and Silas, who shall also tell you the same things by mouth." (Emphasis mine).
Thus, as far as this conversation goes, tradition is specifically teachings and practices passed down by the Catholic Church. The idea that the Apostles preached other things that the scriptures do not cover is simply not supported by scripture, and evidently wasn't believed by the early Church either. Indeed, it was seen as flat out heretical to believe one could add to God's words. Thus, it is necessary to isolate Catholic tradition, and so what we are ultimately asking is which is more authoritative: Catholic tradition, or scripture?
What is scripture?
But what is scripture? In short, scripture is a written work which is divinely inspired by God. In fact, the actual word used to describe this concept in scripture is "theopneustos" (θεόπνευστος), which means "God breathed". This actually leaves Catholics with a dilemma. According to Catholic doctrine, the criteria for what is scripture is the "infallible" decision of the Church, effectively allowing the Catholic Church to decide when a written work is inspired or not. Even the dispute over the canonical status of the Deuterocanon was not "settled" until the Council of Trent (3). This, however, defies common sense, not only because it requires the literal changing of the past, but because it also gives the Catholic Church license to pick and choose when to obey God. For sake of cutting out a lengthy argument, we will simply limit our definition of scripture to our common ground: The "Protestant" canon.
So which is more authoritative?
Suffice to say, the inspiration of scripture alone means scripture cannot be rivalled by anything. Thus, to say something like, for example, "We are better to be without God’s laws than the Pope’s", as it is recorded that one Catholic clergyman said to William Tyndale (4) is pure blasphemy.
But obviously, most Catholics will not say that their Church is above the scriptures. Indeed, on paper, they are not allowed to. In order to be consistent with their doctrine, Catholics must believe "both Sacred Tradition and Sacred Scripture are to be accepted and venerated with the same sense of loyalty and reverence" (5). The problem is, owing entirely to the constant conflict between Catholic doctrine and scripture, this teaching must stay on paper.
What's the Catholic solution?
The Catholic response to any and all contradictions between their doctrines and the scriptures is to, as non-explicitly as possible, state that the Catholic Church is more authoritative than the scriptures. They do this in the same way virtually all other heretics, and even many unbelievers do. That is, of course, the "interpretations" defence. According to Catholic tradition, the scriptures ought not be studied individually (and indeed, there was a time when they violently banned the Bible). Catholics must interpret the scriptures according to the teachings of the Catholic Church. Not even their own senses are considered valid. All of this is blasphemous, for it neither "venerates scripture with the same sense of loyalty and reverence" as tradition, nor places tradition in its proper place, far below scripture. Rather, it argues that, since scripture is open to interpretation, tradition must be higher than scripture, in order to "interpret" it for you.
Of course, in reality, scripture is not open to interpretation. There is a correct interpretation, and there are many incorrect interpretations. This is where the Catholic Church gets a bit too big for its boots. Pointing to the large number of incorrect interpretations, Catholics posit the need for an authoritative body to interpret the scriptures for us. There are a great many problems with this argument (see here, and here, for example), but some of them like to back it up by appealing to the so-called Church "Fathers". It is alleged that the best way to interpret scripture is to do it using the opinions of the early Church. It is argued that, since the Church "Fathers" lived closer to biblical times, some of them even having been personally taught by the Apostles, their interpretations are of great worth.
What is the Christian solution?
There are a number of ways to respond to this argument, including the rather sarcastic jab I fired at a Catholic, as seen in the screenshots to the left of this paragraph. As you can see, I reversed his logic, and highlighted the inconsistency of the argument. See, if we cannot adequately interpret the divinely inspired scripture, which according to its own words gives understanding to the simple (Psalm 119:130), how are we supposed to interpret the uninspired Church "Fathers"?
And that's where we get to beat Catholics at their own game. It is utter blasphemy to use man's word to reinterpret scripture, but it is entirely permissible to use God's word to overrule man. But why not take it one step further? If Catholics are allowed to say silly things like "Church Father X knew the Apostles", why can we not say "God knows Church Father X"?
Now, we could just let the Catholic Church be themselves, accepting their teachings when they're right, rejecting them when they're wrong, but why don't we have some fun? Let us swear our allegiance to the Catholic Church, but with a Godly twist. Every time the Catholic Church conflicts with the Bible, let us reinterpret their teachings until they align with scripture. Even the so-called Church "Fathers" did not have everything right (even by the Catholic Church's own admission). They taught numerous strange, even detestable things. But maybe, we can start to simply reinterpret them, rather than reject them.
Going back to our original question "which is more authoritative?", the answer is indisputably scripture. Scripture is divinely inspired, Catholic tradition is not. Thus, by the simple fact that God, who has all authority in Heaven and on Earth, inspired the scriptures, the scriptures are more authoritative, and the fact that the Catholic Church claims otherwise is one more proof that it is not the one true Church Christ started.
References
1. Dictionary.com - Tradition, entry 2 (link)
2. Irenaeus - Against Heresies
3. The New Catholic Encyclopedia, The Canon
4. william-tyndale.com (link)
5. Pope Paul VI - Dogmatic Constitution on Divine Revelation, Dei Verbum, Chapter 2, November 1965