I think your question is too broad because it's too easy to confuse the different aspects of proprietary, free, commercial, source available, no cost, support c

I think your question is too broad because it's too easy to confuse the different aspects of proprietary, free, commercial, source available, no cost, support contract, and volunteer support. Why not narrow it down? Which do you think is more secure, the open source Darwin operating system or the proprietary Mac OS X?