1. Ontology should be the starting point for Christian education, for it is only insofar as we know what is God and what is man that we can know who is Christ as Lord and Savior.
2. Epistemology should be the starting point for Christian apologetics, for it is only insofar as we can justify our claims to the truth as well as our refutations of error that the unbeliever can be shown foolish, and the wisdom of God be acknowledged as true.
As a student of rhetoric I have a suspicion that one of the chief causes for the differences between Cornelius Van Til and Gordon Clark was in the context and audience of the development of their thought. Van Til taught at a reformed seminary where appeals to the Word of God and the basic knowledge of God were as common and acceptable as tap water. Clark taught for almost three decades in the philosophy department at Butler University, an institution of Christian heritage, but not directly governed by any ecclesiastical authority.
There is a different emphasis when one addresses an audience who is in basic agreement, particularly on a presuppositional level, than when one addresses an audience is in basic opposition. While I don't think this observation minimizes the differences between the two apologists, I do think it helps to explain why they developed their thoughts differently, despite being very close in the actual way in which they refuted opponent arguments.
Van Til wanted to begin with the being of God; Clark with the knowledge of God. Van Til was following the Dutch tradition of the Heidelberg Catechism; Clark was following Calvin and the Westminster Confession of Faith.
I think there is value in both approaches, but I think that audience matters, and thus I would defend the two theses at the top as the preferred approach for a sympathetic and unsympathetic audience, respectively.