Is it correct to marry a beautiful woman who is ordinarily religious, hoping to change her for the better after marriage, or is it better to marry a woman who is already religious, taking into account the woman's age and other factors influencing susceptibility to change?

A religious woman is the best for marriage. She is the most capable of safeguarding her husband and protecting him in himself, his wealth, and his children, and she avoids disobedience. This is in accordance with the Almighty’s saying: "So righteous women are devoutly obedient, guarding in [the husband's] absence what Allah would have them guard." If beauty and lineage are combined with religiosity, that would be even better.

Regarding the "ordinarily" religious girl: If what is meant is that she is not upright, then marrying her with the intention of reforming her is not sound, as her situation may not change, or she may negatively influence him. However, if she is upright but lacks perfect uprightness, then there is no harm in marrying her while striving to teach and remind her, and for the husband to be an example for her.