CBC and Symphony for open-source MILP, Gurobi for commercial MILP. OR-Tools for some VRP work. I use R (ompr package) to interface to CBC, Symphony, and Gurob

CBC and Symphony for open-source MILP, Gurobi for commercial MILP. OR-Tools for some VRP work. I use R (ompr package) to interface to CBC, Symphony, and Gurobi. HiGHS is looking promising.