Asymmetric international mobility of highly talented scientists is well documented. We contribute to the explanation of this phenomenon, looking at the "competitiveness" of research universities in terms of being able to attract talented early stage researchers. We propose a new hybrid quantitative-qualitative methodology for comparing the top tier of national higher education systems: We characterise a country's capability to offer attractive entry positions into academic careers building upon the results of a large scale experiment on the determinants of job choice in academia, using a mix of data and expert-based assessment. We examine salary level, quality of life, career perspectives, research organisation, balance between teaching and research, funding and the probability of working with high quality peers. Our results in the form of a job attractiveness index indicate that overall, the US research universities offer the most attractive jobs for early stage researchers, consistent with the asymmetric flow of talented scientists to the US. By comparison with rankings that use survey results or bibliometric data, our methodology offers the advantage of comparing structures and factors shaping the process of research rather than results of research. The findings are hence directly relevant for policies aiming at improving the attractiveness of research universities.