Doing MS in CS from low ranked university versus applying again next year?
(1) Should I accept going to low/no rank university now or should I try again next year?


You must go to USA first. The world is changing every now and then. You never know what will happen next year. You can have the Visa, go there, and, you will always have the opportunity to change your university.


  (2) is it okay to request the university to defer the admission for a year so that I can apply for better universities next year?


If the university has a provision to do so, they will. For example, I got acceptance from UCD, Dublin, Ireland. They have a provision to do so. So, I paid the registration fee and they reserved my acceptance for the next year. But, It is highly unlikely that I would go there.