adding you to his american express account although nice, will not help your credit. As you are only added as an authorised user. And lenders to add that in to your score as you are not finacially resposible for the account. I would keep the AMEX account, as you will eventually get a unsecured card from them , and earn interest on your money at the same time. Just my opinion. Also another thing to take in account is that lenders tend to look unfavorable at alot of closed accounts right after opening. It's best to keep them awhile then close them.