Scoring wise, you have to pay the closed BoA account and have it report a zero balance...closed accounts with balances hurt your scores and do factor in util% calculations. To minimize the hit to your scores USA bank would be better.
IMHO, saving money is more important! I would go the Amex route but be very careful. Amex hates card holders who revolve high balances. To avoid any problems with Amex make large timely payments.