It has been running our simulations of over 1 million vehicle fleet scenarios for almost 7 years now with great results! I think Gurobi is the best on the market. We are solving large scale nonlinear mixed integer programs (MIP) in less than 5 seconds on a desktop computer with no special hardware or software required. There are certain functions like "get_feasible" that work well and fast but have a small drawback - they don't support multiple input files at once but rather process them one by one. The MIP solver handles very large size instances without slowing down.