AMEX Starwood Preferred Guest (SPG) is a good card because it allows you to transfer Starpoints to airline miles with bonus (eg transfer 20K Starpoints for 25K airline miles). There's a promo going on right now where you can get up to 25K Starpoints. There is an annual fee however, but it's waived for the first year. And since you're churning, I'm assuming you won't keep it for long