The ringdown part of gravitational waves in the final stage of the merger of compact objects tells us the nature of strong gravity and hence can be used for testing theories of gravity. The ringdown waveform, however, fades out in a very short time with a few cycles, and hence it is challenging to extract the ringdown frequency and its damping timescale. We here propose to build up a suite of mock data of gravitational waves to compare the performance of various approaches developed to detect the dominant quasinormal mode from an excited black hole after merger. In this paper, we present our initial results of comparisons of the following five methods: (1) plain matched filtering with ringdown part method, (2) matched filtering with both merger and ringdown parts method, (3) Hilbert-Huang transformation method, (4) autoregressive modeling method, and (5) neural network method. After comparing the performances of these methods, we discuss our future projects.