There is no right and wrong answer however I always put most of my spend on the Amex card and then I pay it off every month. I use it just as my debit card. Occasionally when there is a good sign up bonus I will sign up for a card keep it for as long as it’s needed and then cancel. I always pay my card in full and never accumulate interest. This number one is haram (non permissible) in Islam and number two there is no benefit for you as you are actually going to pay for the bonus you receive.