grammar - When is it okay to not use a comma before an 'and' or 'or' followed by an independent clause?

I punched him and he cried.

or

I punched him, and he cried.

Are both acceptable? Is one better than the other? Personally, I like the first one best, as it better shows the cause/effect relationship of the two clauses, but I am not confident that it is gramatically correct.

He told me to do it or I would have to leave.

or

He told me to do it, or I would have to leave.