Business rules (BR’s) play a critical role in an organization’s daily activities. With the increased use of BR (solutions) and ever increasing change frequency of BR’s the interest in modifiability guidelines that address the manageability of BR’s has increased as well. A method of approach to improve manageability and modifiability is to utilize architectures to structure BR’s. In current literature three different methods to structure business rules can be identified: 1) the rule family-oriented approach, 2) the fact-oriented approach and, 3) the decision-oriented approach. Scientific research comparing the ability to modify business rules in each of the three architectural candidates is limited. The goal of this research is to evaluate which architectural candidate and underlying architectural structures allow for the best modifiability. We sought to do so by applying design science research for the creation of the architectural candidates and by conducting semi-structured interviews to identify the case-specific productivity scores. By applying an Architecture-Level Modifiability Analysis using eight years of historical data from the British National Health Service each architectural candidate is evaluated with regards to its modifiability. Results of the analysis reveal that the rule family-oriented architecture scores best on modifiability, followed by the fact-oriented architecture, and lastly the decision-oriented architecture. The results of this study provide a foundation for further research on the application and evaluation of business rule architectures.