This paper focuses on the benchmarking that is one of the main issues of the synthesis method and tool development, analysis, characterization and evaluation. To solve several serious problems related to the usage of practical industrial benchmarks, we developed and implemented an FSM Benchmark Generator (BenGen). BenGen makes us possible to efficiently construct FSMs with various known characteristics, including FSMs representative to various typical industrial application areas, greatly reduces the necessity of having the actual industrial benchmarks, and enables research, comparison, evaluation and fine tuning of circuit synthesis methods largely independent of the industry, and much more effectively and efficiently than having only some industrial benchmarks. Using a large set of benchmarks generated with BenGen, we performed an experiment aiming at the effectiveness characterization of some popular academic and industrial FSM state assignment approaches. The experimental results enabled us among others to demonstrate that the pragmatic assignment approaches used commonly in today's commercial tools are only effective for some special classes of circuits or not effective at all.