Most Effective

The most effective debugging tool is still careful thought, coupled with judiciously placed print statements.

-- Brian Kernighan (1 January 1942 -), computer scientist who worked at the Bell Labs and contributed to the design of the pioneering AWK and AMPL programming languages, most well-known for his co-authorship, with Dennis Ritchie, of the first book on the C programming language, "Unix for Beginners" (1979)