I'm going to vote for answer (C) Don't bother.
They're largely unnecessary. Personally, I never bother to look at them when they are provided.
They're unnecessary before development, because the design will change anyway. And if you don't think the design of your classes will change, then you're already handcuffing yourself and preventing your future self from being able to properly solve the problem. If you think you have to stick to some pre-existing class diagrams, then you either work for NASA or you're shooting yourself in the foot.
Afterwards, they're unnecessary documentation. If you can't figure out what the classes are doing or how they're related to each other with a little code inspection, then you have a hole in your skill set as a software developer.
Of course, this answer sounds really arrogant and opinionated; oh well.