Some background: I have no debt, have never carried a balance on the card, and have never used more than 10-15% of the credit limit per month. I'd much prefer to pay with debit/cash, but I got the credit card (BofA Visa) to establish some credit history so that I could be approved for a mortgage. I've had the card for about 6 months, but for various reasons I have switched my checking and savings to USAA. For mostly convenience reasons (and because I can use it at Costco!) I would like to switch to a USAA Amex card.
I know that cancelling a credit card can affect my credit score, but what are the circumstances in which it will do so? Given that I have never carried a balance, etc., will cancelling the card definitively hurt/help my credit score? Am I better off just keeping the card forgetting about it?