[yablak]

You're probably looking for a performance comparison. Look here:

http://plato.asu.edu/bench.html

This one stays pretty well updated. On the MIP side:

  * COPT
  * SCIP
  * HiGHS

seem to be top performers (of the OSS variety).

IIRC OR-Tools often by default uses SCIP for its MILP backend.

[SparseRunner]

The latest results show HiGHS to be significantly better than vanilla SCIP. If "OSS" means "Open Source Solvers" then COPT isn't open-source and SCIP isn't open source for commercial purposes. Hence the warning given by OR-Tools. HiGHS is very much the best bet going forward for open-source MIP