Currently, WindSim 12 supports GCV, Parallel GCV, GCV-AMG and Parallel GCV-AMG solvers. Selecting the solver depends on your project configurations and size. We can not say which solver is exactly the best. Based on our tests, GCV solver is one of the best in most of the tests. For big projects (more than 4 M cells), Parallel GCV or Parallel GCV-AMG and RNG K-ɛ turbulent model could be fastest option. But users should keep in mind that reaching convergence criteria depends on several factors such as terrain complexity, turbulent models, boundary conditions and etc. and can be different for different projects.