Which of the two names may be used for the legal marital contract of a person who has two names, one for personal use and the other official with the state?

There is no harm in changing a name for a benefit, or in a person having two names, as Jacob (peace be upon him) had two names, and the Prophet (peace and blessings of Allah be upon him) had five names. It is permissible to mention either of the two names at the time of marriage as long as the person is known by both. However, it is preferable to record the name mentioned in official documents, especially if the other name is merely a title.