After collecting several boxes of the MH Model PLUS Volume sets, we did some backtrack and started searching for previous volumes. So far what we've found is this best of 4, 5, 6 box set. As the name implies, it's a compilation of the popular monster from vol. 4, 5, and 6. These monsters include Lagiacrus, Nargacuga, Brachydios, Rathalos, Azure Rathalos, Rathian, Pink Rathian, Zinogre and Stygian Zinogre.
Unlike the PLUS series, the BEST series doesn't come with a secret monster. Rather, it's already a box set of 9 monsters compared to the 6+1 box set of the PLUS series. Each individual box is a bit smaller compared to that of the PLUS series. Hopefully, we'll be able to complete the BEST series.