Must/have to

Which of the modal verbs (have to or must) is preferable in the situations like these:
You must/have to fasten your seat belt while driving?
You must/have to stop at the STOP sign.

The law says you must/have to pay the taxes.

In such situations we can refer the action to the law. And if we break it, we will be punushed, fined etc. But at the same time it can be considered as a strong order. Or must is used only with the shade of someone's personal opinion and only have to is possible here?