As someone who had all accounts as joint accounts for years, I can say you should keep them separate. That way if something happens you may not need to ruin both your credit to recover. As Medic said you can always add each other as AU's on the cards, but I don't even do that any longer.
I'd keep cards separate and do joint on loan only if one person's income would not be considered sufficient
Each consumer, even if they are spouses, have separate credit files.
Each consumer only has the right (absent a separate power of attorney) to access and update or correct their own credit file and credit report.
Joint accounts can appear in the credit file of each consumer.
However, consumer A cannot use a joint account status to dispute, for example, reporting to the file of consumer B.
Simply stated, you each conduct your own rebuilding as related to your credit report.