If 直系亲属 is your sister or brother, then you can show that you will come back China because your parents or your own family (spouse & Child) are still in China;
If all your 直系亲属 are in US (for example, your brother may be a citizen and applying greencards for your parents; or your parent is US citizen or PR) , then you will have 移民倾向; So the best way is ask 直系亲属 to find an American friend to 担保. (you have to think about a good expalnation - how they know you or your parents);
I think that 房子证明 is better than 银行证明 because 房子证明 is a better proof that you will go back China.