In medical ultrasonography, speckle model parameters are dependent on scatterer density and regularity, and can be exploited for use in tissue characterization. The purpose of the current study is to quantify the goodness-of-fit of two models (the Nakagami and K distributions), applied to envelope data representing a range of clinically relevant scattering conditions. Ground truth data for computing goodness-of-fit were generated with envelope simulators. In the first simulation, 100 datasets of various sample sizes were generated with 40 scatterer densities, ranging from 0.025 to 20. Kolmogorov-Smirnov significance values quantified the goodness-of-fit of the two models. In the second simulation, densities ranged from 2 to 60, and additional scattering parameters were allowed to vary. Goodness-of-fit was assessed with four statistical tests. Although the K distribution has a firm physical foundation as a scattering model, inaccuracy and high standard deviation of parameter estimates reduced its effectiveness, especially for smaller sample sizes. In most cases, the Nakagami model, whose parameters are relatively easy to compute, fit the data best, even for large scatterer densities.