You will get a seat based on your category. A UR candidate can not take the seat of a vacant SC candidate which is why streamlining and simplifying the process is very important. During counselling, both of your ranks are considered as your AIR directly determines your category rank.

If counselling is considered strictly based on merit, AIR is important. But since candidates and seats are divided based on different categories, the category rank is important. So your category rank will be given more importance because of the seat matrix.