You should enter your obc ncl rank  in the option provided in the predictor. Choose it under the category section. It is quite obvious that you should enter the rank which shall help you in getting the reputed colleges which you can get with your obc rank only. Entering the general rank will hamper your chances of getting in reputed institutions.

So, clearly you must enter your obc ncl rank in the category section in the college predictor. Hope this resolves your query.