First of all let me make it clear that I am glad that this choice is not laid out before us, but if I had the choice of having only the Old
Testament, or only the New Testament, I would take the Old Testament. I suppose that sounds absurd at the outset, especially for someone who is firmly Christian and utterly convinced of the doctrine laid forth in New Testament, and one who views the entire New Testament as authoritative scripture, nonetheless it is true.
The implications of what I am saying are a bit startling at first. I am essentially saying that, in some sense, if I were to have to make the decision between Romans and the Pentateuch, I take the Pentateuch. Allow me to explain:
One of the practices I engage in as I read works of theology is the practice of chasing references. For instance I have found that most of the contemporary authors that I enjoy reading are frequently quoting CS Lewis, naturally as I read them I am impelled to go back and read Lewis to see what the contemporary authors are referring to. What I end up coming to realize is that by reading Lewis, and then going back further to Luther, and Calvin, Augustine, and *gasp* even Wesley… is that I begin to generate the same conclusions that contemporary authors are writing about. In other words, if I go to the source documents I actually begin to develop the same thought patterns that are driving contemporary authors. By doing this you become less and less dependent on the current works being churned out because they are merely churning out the same thoughts that you are already developing because you are drawing from the same sources.
Logically if you continue to do this eventually you end up back to Paul and the other New Testament authors, but quickly you come to realize that their source documents are that of the Old Testament. In other words you begin to find that the New Testament is merely the expounding of the Old Testament in light of the historical reality of the life, death, and resurrection of Christ. In other words, if you follow the practice of chasing the source documents you will eventually find yourself resting on the bedrock of it all, which is the Old Testament scriptures.
Consider the verse:
16 All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness, 17 that the man of God may be competent, equipped for every good work. 
Paul writes this passage long before the New Testament is canonized as scripture, and is clearly referring to the Old Testament scriptures. The similar case can be made for Hebrews 4:12. The bottom line is that the Old Testament scripture is given prominence even within the New Testament, and the New Testament never asserts itself over and above the old.
What then of the epistles? Paul writes them explaining the reality of what Christ’s life, death, and resurrection mean in light of the Old Testament. Without the New Testament I can still document the reality of Christ’s life death and resurrection as verifiable historical events, and I can read the Old Testament in light of those events. The writings of the New Testament give us an example of how to go about utilizing the Old Testament texts in light of Christ. Just like reading John Piper gives us insight into understanding CS Lewis and Jonathan Edwards in our day, Paul gives us insight into the Old Testament in light of Christ’s work. If we are firmly aware of Christ’s work on our behalf, we can go to the source documents (The Old Testament) with fresh understanding, knowing that the OT is sharper than any two edged sword, and knowing that it is God breathed, and profitable for teaching, reproof, correction, and training in righteousness.
With all that said, God forbid I ever be forced to choose between the new and the Old Testament! What I am saying though is that the New Testament has trained me to be able to read the old. God forbid I have to give up contemporary authors, they have aided my understanding of those who have gone before. However if I had to choose to have only Piper and Horton, or only Lewis and Edwards… I am taking Lewis and Edwards… and if I had to choose between only the New Testament or only The Old Testament, I am taking the Old. (Of course, this assumes that I can still have a historical record of the life, death, and resurrection of Christ, which could raise the debate as to whether the Gospels should be New or Old Testament, but that is for another time.)
 The Holy Bible : English standard version. 2001 (2 Ti 3:16–17). Wheaton: Standard Bible Society.