Normally, the answer to that question depends on whether you're going to run an exhaust manifold or headers. Generally speaking, exhaust manifolds get split patterns and headers get single. But that's not set in stone at all. For example, right now, the current engine I have in Vixen has an exhaust manifold with a single pattern camshaft. The current build I am working on will have headers and a split pattern camshaft because "that's what I want".