Husband & Wife credit have many options. However, joint credit is usually not a good one.
Your strategy will have many factors. Which of the two has credit, one or both or none? Will you be carrying any balances?
If one has credit established and the other not, then adding the one without credit as an AU help to establish a credit profile, improves average age of accounts and will help them when obtaining credit in their own name, which they do need to do.
If neither has credit, then AU is of no help, in fact it hurts. Adding each other as AU only increases the number of new accounts and does not improve account ages. So, if both are new to credit, I would suggest maintaining independent credit without AU.
If both have established credit, AU can go either way depending on CL's and carrying balances. For example, if both have established credit, but one has much greater CL's, then it may be good to add the spouse as an AU to one of the higher CL accounts.
Also, if you will be carrying any balances, the AU can be used to help utilization. For example, if a balance will be carried, you may elect to put the balance on the husband's card. This will hurt his utilization. You can then add the husband to a card or two of the wife's (these need to be cards that report zero balance). The addition of these accounts CL's with zero balance will soften the percentage of utilization of the balance carried.
Finally, joint credit is almost always a bad idea for many many reasons. If ever there is a financial problem which affects credit, joint credit will hit both spouses, whereas if you maintain individual credit you may be able to isolate it to one spouse and still have the other's to use going forward.
God forbid a divorce, but if all credit is joint, upon divorce those accounts will most likely be closed meaning that you are starting over. If the wife only has AU credit, she will have no credit of her own (and vice versa sometimes).