The research in this paper does not result in any conclusive evidence that says TDD is better, it merely showed that TDD encourages developers to work longer until a higher code quality is attained. If I read it correctly.
It's going to be impossible to quantify "better" anyways. It depends on what you're optimizing for. This research is incredibly valuable in helping us understand the results of TDD, particularly if we're optimizing purely for quality:)