Most bug-free Operating System I have used is Windows 3.11, and if it crashes, you just press CTRL+ALT+DEL and it would tell you the problem and then you would simply press ENTER to fix it.
Linux, I would call it FAR From bug free. I dont use the Desktop Linux distributions for a good reason, I've never gotten along with them, and advanced configuration is a pain.
I've always stuck with Windows since it can do what I need it to do, unlike Mac or Linux. I can use the programs that I want to use, and I can configure it the way I want.
Bug wise, you have to consider:
Often its not bugs in the operating system, its a bug in the program you are trying to run in the operating system.
One thing I liked about DOS is you only run one thing at once, and it runs in its own little environment, and it has no conflict with the OS since DOS was so defined and it never had problems with other programs either.