I am engaged and wondering,
should I have a personal and joint account, or just a joint account.

    I want to commend you both for desiring a joint account as a married couple.  This action goes a long way to promoting the "oneness" that is so essential in a marriage relationship, but I am thinking your actions might be premature.  I have never been confronted with your question and thus considered the issue from God's point of view, so I cannot speak definitively on the matter.  What I will offer is a best guess, but  I encourage you to seek the counsel of someone formally trained in theology.

    In the days and culture of Jesus, being engaged took on a very much more significant meaning than today.  It was tantamount to being married.  So much so, that when Joseph found out that Mary was pregnant, he considered divorcing her secretly to avoid her additional grief and shame.  Today, we would not think of using the term "divorce" to end an engagement.  We would just "call it off."  There is usually little or no legal binding in today's engagements.

    If you open a joint account, you will likely only fall under the applicable laws governing such action irrespective of your engaged status.  Legally you will probably be considered as just two adults consenting to open a joint account and each be held liable for it.  As an engaged couple, it would not surprise me in the least if your theologically trained counselor tells you that God's law now considers the man as the head of the engaged woman and as such is responsible for their finances.  Thus, a joint account would make perfect sense.

    What concerns me is having both a personal and joint account.  Spilt accounts is just the sort of signal that I frequently see with couples who come to see me when they are in trouble.  It suggests to me that each person is attempting to maintain a sense of independence from the other.  For the husband to do this suggests that he desires to withhold provision and blessing from his wife, and for the wife to have a personal account suggests that she desires to maintain a separate source of provision apart from her husband.  If one or both engage in this behavior, the oneness that is essential to marriage is undermined and a false image of the relationship which Christ has with us (His bride) is being promoted by their style of marriage relationship.  So, I suggest that if your theology adviser endorses a joint account, have only a joint account, not a mix.