No requirements technique works for all applications. The requirements for complex applications can be best understood when multiple techniques are used. Use a technique or set of techniques most appropriate for your application.
For example, use entity-relation diagrams for data-intensive applications, finite state machines or statecharts for reactive (real-time) systems, Petri nets for applications with synchrony challenges, decision tables for decision-intensive applications, and so on.
Reference:
Davis, A., "A Comparison of Techniques for the Specification of External System Behavior," Communications of the ACM, September 1988.
