Look at point earning rules. IIRC using the SPG credit card to pay results in an additional point per dollar as does Gold status, but please check this.

If you often travel together, it can make sense to concentrate night/stay credits to a single account to maximize status, with the credits going to the person who is most likely to travel alone. IIRC the SPG credit card gives you a few night and stay credits evey year, so consider that too, but I'm not sure how partial years arer treated on this.

ADDED: People from the SPG forum on FT should be able to give you more detailed advice. You ccan ask a mod to move the thread, but please do not double post.